Surgical system and procedure for precise intraocular pressure reduction

ABSTRACT

An initial treatment pattern defining an initial volume of ocular tissue to be modified for treating glaucoma is designed. An initial laser treatment is delivered by scanning a laser beam across ocular tissue at an initial placement in the eye in accordance with the initial treatment pattern to thereby photo disrupt the initial volume of ocular tissue. A postoperative measure of intraocular pressure (IOP) is evaluated relative to an IOP criterion to determine if the treatment was successful. If the treatment was not successful, meaning the IOP criterion was not satisfied, then a subsequent treatment pattern that defines a subsequent volume of ocular tissue to be modified, and/or a subsequent placement in the eye is determined. A subsequent laser treatment is delivered by scanning a laser beam across ocular tissue at the subsequent placement within the eye in accordance with the subsequent treatment pattern to thereby photo disrupt the subsequent volume of ocular tissue.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a divisional application of U.S. patent application Ser. No. 16/125,597, filed Sep. 7, 2018, for “Surgical System and Procedure for Precise Intraocular Pressure Reduction,” the entire disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to the field of medical devices and treatment of diseases in ophthalmology, and more particularly to systems, apparatuses, and methods for precise intraocular pressure reduction, for the laser surgery treatment of glaucoma.

BACKGROUND

Before describing the different types of glaucoma and current diagnosis and treatments options, a brief overview of the anatomy of the eye is provided.

Anatomy of the Eye

With reference to FIGS. 1-3 , the outer tissue layer of the eye 1 includes a sclera 2 that provides the structure of the eye's shape. In front of the sclera 2 is a cornea 3 that is comprised of transparent layers of tissue that allow light to enter the interior of the eye. Inside the eye 1 is a crystalline lens 4 that is connected to the eye by fiber zonules 5, which are connected to the ciliary body 6. Between the crystalline lens 4 and the cornea 3 is an anterior chamber 7 that contains a flowing clear liquid called aqueous humor 8. Encircling the perimeter of the crystalline lens 4 is an iris 9 which forms a pupil around the approximate center of the crystalline lens. A posterior chamber 10 is located between the crystalline lens 4 and the retina 11. Light entering through the cornea 3 is optically focused through the crystalline lens 4.

With reference to FIG. 2 , the corneoscleral junction of the eye is the portion of the anterior chamber 7 at the intersection of the iris 9 and the sclera 2. The anatomy of the eye 1 at the corneoscleral junction includes a trabecular meshwork 12. The trabecular meshwork 12 is a fibrous network of tissue that encircles the iris 9 within the eye 1. The base of the trabecular meshwork 12 and the edge of the iris 9 are attached together at the scleral spur 14. The network of tissue layers that make up the trabecular meshwork 12 are porous and thus present a pathway for the egress of aqueous humor 8 flowing from the anterior chamber 7. This pathway may be referred to herein as an aqueous humor outflow pathway, an aqueous outflow pathway, or simply an outflow pathway

Referring to FIG. 3 , the pathway formed by the pores in the trabecular meshwork 12 connect to a set of thin porous tissue layers called the uveal 15, the corneoscleral meshwork 16, and the juxtacanalicular tissue 17. The juxtacanalicular tissue 17, in turn, abuts a structure called Schlemm's canal 18. The Schlemm's canal 18 carries a mixture of aqueous humor 8 and blood from the surrounding tissue to drain into the venous system though a system of collector channels 19. As shown in FIG. 2 , the vascular layer of the eye, referred to as the choroid 20, is next to the sclera 2. A space, called the suprachoroidal space 21, may be present between the choroid 20 and the suprachoroidal space 21. The general region near the periphery of the wedge between the cornea 3 and the iris 9, running circumferentially is called the irido-corneal angle 13. The irido-corneal angle 13 may also be referred to as the corneal angle of the eye or simply the angle of the eye. The ocular tissues illustrated in FIG. 3 are all considered to be within the irido-corneal angle 13.

With reference to FIG. 4 , two possible outflow pathways for the movement of aqueous humor 8 include a trabecular outflow pathway 40 and a uveoscleral outflow pathway 42. Aqueous humor 8, which is produced by the ciliary body 6, flows from the posterior chamber 10 through the pupil into the anterior chamber 7, and then exits the eye through one or more of the two different outflow pathways 40, 42. Approximately 90% of the aqueous humor 8 leaves via the trabecular outflow pathway 40 by passing through the trabecular meshwork 12, into the Schlemm's canal 18 and through one or more plexus of collector channels 19 before draining through a drain path 41 into the venous system. Any remaining aqueous humor 8 leaves primarily through the uveoscleral outflow pathway 42. The uveoscleral outflow pathway 42 passes through the ciliary body 6 face and iris root into the suprachoroidal space 21 (shown in FIG. 2 ). Aqueous humor 8 drains from the suprachoroidal space 21, from which it can be drained through the sclera 2.

Aqueous humor 8 outflow through the trabecular outflow pathway 40 is pressure dependent in that outflow increase as the intraocular pressure increases, whereas aqueous humor 8 outflow through the uveoscleral outflow pathway 42 is pressure independent. Resistance to the outflow of aqueous humor 8 through the trabecular outflow pathway 40 may lead to elevated intra-ocular pressure of the eye, which is a widely recognized risk factor for glaucoma. Resistance through the trabecular outflow pathway 40 may increase due a collapsed Schlemm's canal 18 or the presence of a high density of collector channels 19.

Referring to FIG. 5 , as an optical system, the eye 1 is represented by an optical model described by idealized centered and rotationally symmetrical surfaces, entrance and exit pupils, and six cardinal points: object and image space focal points, first and second principal planes, and first and second nodal points. Angular directions relative to the human eye are often defined with respect to an optical axis 24, a visual axis 26, a pupillary axis 28 and a line of sight 29 of the eye. The optical axis 24 is the symmetry axis, the line connecting the vertices of the idealized surfaces of the eye. The visual axis 26 connects the foveal center 22 with the first and second nodal points to the object. The line of sight 29 connects the fovea through the exit and entrance pupils to the object. The pupillary axis 28 is normal to the anterior surface of the cornea 3 and directed to the center of the entrance pupil. These axes of the eye differ from one another only by a few degrees and fall within a range of what is generally referred to as the direction of view.

Glaucoma

Glaucoma is a group of diseases that can harm the optic nerve and cause vision loss or blindness. It is the leading cause of irreversible blindness. Approximately 80 million people are estimated to have glaucoma worldwide and of these, approximately 6.7 million are bilaterally blind. More than 2.7 million Americans over age 40 have glaucoma. Symptoms start with loss of peripheral vision and can progress to blindness.

There are two forms of glaucoma, one is referred to as closed-angle glaucoma, the other as open-angled glaucoma. With reference to FIGS. 1-4 , in closed-angle glaucoma, the iris 9 in a collapsed anterior chamber 7 may obstruct and close off the flow of aqueous humor 8. In open-angle glaucoma, which is the more common form of glaucoma, the permeability of ocular tissue may be affected by blockage of tissue in the irido-corneal angle 13 along the trabecular outflow pathway 40 or by the collapse of the Schlemm's canal 18 or collector channels 19.

As previously stated, elevated intra-ocular pressure (IOP) of the eye, which damages the optic nerve, is a widely recognized risk factor for glaucoma. However, not every person with increased eye pressure will develop glaucoma, and glaucoma can develop without increased eye pressure. Nonetheless, it is desirable to reduce elevated IOP of the eye to reduce the risk of glaucoma.

Methods of diagnosing conditions of the eye of a patient with glaucoma include visual acuity tests and visual field tests, dilated eye exams, tonometry, i.e. measuring the intra-ocular pressure of the eye, and pachymetry, i.e. measuring the thickness of the cornea. Deterioration of vision starts with the narrowing of the visual field and progresses to total blindness. Imaging methods include slit lamp examination, observation of the irido-corneal angle with a gonioscopic lens and optical coherence tomography (OCT) imaging of the anterior chamber and the retina

Once diagnosed, some clinically proven treatments are available to control or lower the intra-ocular pressure of the eye to slow or stop the progress of glaucoma. The most common treatments include: 1) medications, such as eye drops or pills, 2) laser surgery, and 3) traditional surgery. Treatment usually begins with medication. However, the efficacy of medication is often hindered by patient non-compliance. When medication does not work for a patient, laser surgery is typically the next treatment to be tried. Traditional surgery is invasive, more high risk than medication and laser surgery, and has a limited time window of effectiveness. Traditional surgery is thus usually reserved as a last option for patients whose eye pressure cannot be controlled with medication or laser surgery.

Laser Surgery

With reference to FIG. 2 , laser surgery for glaucoma target the trabecular meshwork 12 to decrease aqueous humor 8 flow resistance and increase aqueous humor outflow. Common laser treatments include Argon Laser Trabeculoplasty (ALT), Selective Laser Trabeculoplasty (SLT) and Excimer Laser Trabeculostomy (ELT).

ALT was the first laser trabeculoplasty procedure. During the procedure, an argon laser of 514 nm wavelength is applied to the trabecular meshwork 12 around 180 degrees of the circumference of the irido-corneal angle 13. The argon laser induces a thermal interaction with the ocular tissue that produces openings in the trabecular meshwork 12. ALT, however, causes scarring of the ocular tissue, followed by inflammatory responses and tissue healing that may ultimately close the opening through the trabecular meshwork 12 formed by the ALT treatment, thus reducing the efficacy of the treatment. Furthermore, because of this scarring, ALT therapy is typically not repeatable.

SLT is designed to lower the scarring effect by selectively targeting pigments in the trabecular meshwork 12 and reducing the amount of heat delivered to surrounding ocular tissue. During the procedure, a solid state laser of 532 nm wavelength is applied to the trabecular meshwork 12 between 180 to 360 degrees around the circumference of the irido-corneal angle 13 to produce openings through the trabecular meshwork 12. SLT treatment can be repeated, but subsequent treatments have lower effects on IOP reduction.

ELT uses a 308 nm wavelength ultraviolet (UV) excimer laser and non-thermal interaction with ocular tissue to treat the trabecular meshwork 12 in a manner that does not invoke a healing response. Therefore, the IOP lowering effect lasts longer. However, because the UV light of the laser cannot penetrate deep into the eye, the laser light is delivered to the trabecular meshwork 12 via an optical fiber inserted into the eye 1 through an opening and the fiber is brought into contact with the trabecular meshwork. The procedure is highly invasive and is generally practiced simultaneously with cataract procedures when the eye is already surgically open. Like ALT and SLT, ELT also lacks control over the amount of IOP reduction.

None of these existing laser treatments represents an ideal treatment for glaucoma. Accordingly, what is needed are systems, apparatuses, and method for laser surgery treatment of glaucoma that effectively reduce IOP without significant scarring of tissue, so the treatment may be completed in a single procedure and repeated at a later time if necessary.

SUMMARY

The present disclosure relates to a method of treating glaucoma in an eye comprising an anterior chamber, a Schlemm's canal, and a trabecular meshwork therebetween. The method includes designing an initial treatment pattern that defines an initial volume of ocular tissue to be modified, and delivering an initial laser treatment by scanning a laser beam across ocular tissue at an initial placement in the eye in accordance with the initial treatment pattern to thereby photo disrupt the initial volume of ocular tissue. The method further includes evaluating a postoperative measure of intraocular pressure (IOP) relative to an IOP criterion to determine if additional treatment is needed. If the IOP criterion is not satisfied, the method continues by determining a subsequent treatment pattern that defines a subsequent volume of ocular tissue to be modified, and a subsequent placement in the eye. Additional treatment is then provided by delivering a subsequent laser treatment by scanning a laser beam across ocular tissue at the subsequent placement within the eye in accordance with the subsequent treatment pattern to thereby photo disrupt the subsequent volume of ocular tissue. In some cases the subsequent treatment pattern may be identical to the initial treatment pattern and only the placement in the eye is changed. In other cases the subsequent placement may be identical to the initial placement and only the treatment pattern is changed. In still other cases, both the treatment pattern and the placement in the eye are changed. A new measure of postoperative IOP is then obtained and evaluated to determine if further treatment is needed.

The present disclosure also relates to a system for treating glaucoma in an eye comprising a cornea, an anterior chamber, a Schlemm's canal, and a trabecular meshwork therebetween. The system includes a first optical subsystem, a second optical subsystem, and a control system coupled to the second optical subsystem. The first optical subsystem includes a focusing objective configured to be coupled to the cornea. The second optical subsystem including a laser source configured to output a laser beam, and a plurality of components configured to one or more of condition, scan, and direct the laser beam through the focusing objective.

The control system is configured to design an initial treatment pattern that defines an initial volume of ocular tissue to be modified, and to instruct the laser source to deliver an initial laser treatment by scanning a laser beam across ocular tissue at an initial placement in the eye in accordance with the initial treatment pattern to thereby photo disrupt the initial volume of ocular tissue. The control system is further configured to evaluate a postoperative measure of IOP relative to an IOP criterion. If the IOP criterion is not satisfied, the control system determines a subsequent treatment pattern that defines a subsequent volume of ocular tissue to be modified, and a subsequent placement in the eye, and instructs the laser source to deliver a subsequent laser treatment by scanning a laser beam across ocular tissue at the subsequent placement within the eye in accordance with the subsequent treatment pattern to thereby photo disrupt the subsequent volume of ocular tissue. The control system then determines if further treatment is needed by obtaining a new measure of postoperative IOP and evaluating it against the IOP criterion.

The present disclosure also relates to a method of designing a treatment pattern for laser beam delivery to ocular tissue of an eye. The method includes applying one or more of a plurality of preoperative outflow parameters to an aqueous flow model, and modifying the aqueous flow model based on a test treatment pattern. The method further includes obtaining a model IOP based on the modified aqueous flow model, and evaluating the model IOP relative to the IOP criterion to obtain an evaluation outcome. If the evaluation outcome is positive, the method proceeds by designating the test treatment pattern as the treatment pattern. If, however, the evaluation outcome is negative, the method proceeds by modifying the aqueous flow model based on a modified test treatment pattern, obtaining of a new model IOP, and the evaluating of the new model IOP relative to the IOP criterion. The foregoing may be repeated until a positive evaluation outcome is obtained.

The present disclosure also relates to an apparatus for designing a treatment pattern for laser beam delivery to ocular tissue of an eye. The apparatus includes a memory and at least one processor coupled to the memory. The processor is configured to apply one or more of a plurality of preoperative outflow parameters to an aqueous flow model and modify the aqueous flow model based on a test treatment pattern. The processor is further configured to obtain a model IOP based on the modified aqueous flow model, and evaluate the model IOP relative to the IOP criterion to obtain an evaluation outcome. If the evaluation outcome is positive, the processor designates the test treatment pattern as the treatment pattern. If, however, the evaluation outcome is negative, the processor modifies the aqueous flow model based on a modified test treatment pattern, and obtains new model IOP based on the modified aqueous flow model, and evaluates the new model IOP relative to the IOP criterion to obtain an evaluation outcome. The foregoing may be repeated until a positive evaluation outcome is obtained.

It is understood that other aspects of apparatuses and methods will become apparent to those skilled in the art from the following detailed description, wherein various aspects of apparatuses and methods are shown and described by way of illustration. As will be realized, these aspects may be implemented in other and different forms and its several details are capable of modification in various other respects. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of systems, apparatuses, and methods will now be presented in the detailed description by way of example, and not by way of limitation, with reference to the accompanying drawings, wherein:

FIG. 1 is a sectional schematic illustration of a human eye and its interior anatomical structures.

FIG. 2 is a sectional schematic illustration of the irido-corneal angle of the eye of FIG. 1 .

FIG. 3 is a sectional schematic illustration detailing anatomical structures in the irido-corneal angle of FIG. 2 , including the trabecular meshwork, Schlemm's canal, and one or more collector channels branching from the Schlemm's canal.

FIG. 4 is a sectional schematic illustration of various outflow pathways for aqueous humor through the trabecular meshwork, Schlemm's canal, and collector channels of FIG. 3 .

FIG. 5 is a sectional schematic illustration of a human eye showing various axes associated with the eye.

FIG. 6 is a sectional schematic illustration of an angled beam path along which one or more light beams may access the irido-corneal angle of the eye.

FIG. 7 is a block diagram of an integrated surgical system for non-invasive glaucoma surgery including a control system, a femtosecond laser source, an OCT imaging apparatus, a microscope, beam conditioners and scanners, beam combiners, a focusing objective, and a patient interface.

FIG. 8 is a detailed block diagram of the integrated surgical system of FIG. 7 .

FIGS. 9 a and 9 b are schematic illustrations of the focusing objective of the integrated surgical system of FIG. 7 coupled to (FIG. 9 a ) and decoupled from (FIG. 9 b ) the patient interface of the integrated surgical system of FIG. 7 .

FIG. 9 c is a schematic illustration of components of the focusing objective and the patient interface included in FIGS. 9 a and 9 b.

FIGS. 10 a and 10 b are schematic illustrations of components of the integrated surgical system of FIGS. 7 and 8 functionally arranged to form a first optical system and a second optical subsystem that enable access to the to the irido-corneal angle along the angled beam path of FIG. 6 .

FIG. 10 c is a schematic illustration of a beam passing through the first optical subsystem of FIGS. 10 a and 10 b and into the eye.

FIG. 11 a is a schematic illustration of a treatment pattern designed by the integrated surgical system of FIG. 7 to affect a surgical volume of ocular tissue.

FIG. 11 b is a schematic illustration of an outflow pathway characterized by a deep channel opening that results from laser application of the treatment pattern of FIG. 11 a.

FIG. 11 c is a three-dimensional schematic illustration of the outflow pathway of FIG. 11 b.

FIG. 12 is a flowchart of a method of modifying ocular tissue at the irido-corneal angle of the eye.

FIG. 13 is a flowchart of a method of delivering light beams to the irido-corneal angle of the eye along the angled beam path of FIG. 6 .

FIG. 14 a is a schematic illustration of a treatment pattern designed by the integrated surgical system of FIG. 7 to affect a surgical volume of ocular tissue.

FIG. 14 b is a schematic illustration of an outflow pathway characterized by a shallow channel opening that results from laser application of the treatment pattern of FIG. 14 a.

FIG. 14 c is a three-dimensional schematic illustration of the outflow pathway of FIG. 14 b.

FIG. 15 a is a schematic illustration of a treatment pattern designed by the integrated surgical system of FIG. 7 to affect an array of surgical volumes of ocular tissue.

FIG. 15 b is a schematic illustration of an array of outflow pathways, each characterized by a shallow channel opening, that results from laser application of the treatment pattern of FIG. 15 a.

FIG. 15 c is a three-dimensional schematic illustration of the array of outflow pathways of FIG. 15 b.

FIG. 16 a is a schematic illustration of a partially collapsed Schlemm's canal.

FIG. 16 b is a schematic illustration of a treatment pattern designed by the integrated surgical system of FIG. 7 to induce a pneumatic expansion of the Schlemm's canal.

FIG. 17 is a graph displaying the dependence between the rate of entry of the newly formed aqueous humor into the anterior chamber (F) and the rate of outflow of aqueous humor (I) as a function of a pressure differential (Pi−Pe) and collective hydraulic conductivity (C).

FIG. 18 is an electrical circuit model for aqueous flow.

FIG. 19 a is an electrical circuit model of aqueous flow, wherein values of resistors are changed to model the treatment pattern resulting in the deep channel opening shown in FIG. 11 b.

FIG. 19 b is an electrical circuit model of aqueous flow, wherein values of resistors are changed to model the treatment pattern resulting in the shallow channel opening shown in FIG. 14 b.

FIG. 19 c is an electrical circuit model of aqueous flow, wherein values of resistors are changed to model the treatment pattern resulting in the pneumatic expansion of the Schlemm's canal shown in FIG. 16 b.

FIGS. 20 a-20 c are variations of the electrical circuit model of FIG. 18 , wherein circuit components are removed based on one or more assumptions related to aqueous flow.

FIG. 21 is a flowchart of a method of designing a treatment pattern using the aqueous flow model of FIG. 18 .

FIG. 22 is a flowchart of a method of modifying ocular tissue at the irido-corneal angle of the eye using the treatment pattern designed by the method of FIG. 21 .

DETAILED DESCRIPTION

Disclosed herein are systems, apparatuses, and methods for safely and effectively reducing intra-ocular pressure (IOP) in the eye to either treat or reduce the risk of glaucoma. The systems, apparatuses, and methods enable access to the irido-corneal angle of the eye and integrate laser surgery techniques with high resolution imaging to precisely diagnose, locate, and treat abnormal ocular tissue conditions within the irido-corneal angle that may be causing elevated IOP.

An integrated surgical system disclosed herein is configured to reduce intraocular pressure in an eye having a cornea, an anterior chamber, and an irido-corneal angle comprising an aqueous humor outflow pathway formed of a trabecular meshwork, a Schlemm's canal, and one or more collector channels branching from the Schlemm's canal. The integrated surgical system also includes a first optical subsystem and a second optical subsystem. The first optical subsystem includes a window configured to be coupled to the cornea and an exit lens configured to be coupled to the window. The second optical subsystem includes an optical coherence tomography (OCT) imaging apparatus configured to output an OCT beam, a laser source configured to output a laser beam, and a plurality of components, e.g., lenses and mirrors, configured to condition, combine, or direct the OCT beam and the laser beam toward the first optical subsystem.

The integrated surgical system also includes a control system coupled to the OCT imaging apparatus, the laser source, and the second optical subsystem. The controller is configured to instruct the OCT imaging apparatus to output an OCT beam and the laser source to output a laser beam, for delivery through the cornea, and the anterior chamber into the irido-corneal angle. In one configuration, the control system controls the second optical subsystem, so the OCT beam and the laser beam are directed into the first optical subsystem along a second optical axis that is offset from the first optical axis and that extends into the irido-corneal angle along an angled beam path 30.

Directing each of an OCT beam and a laser beam along the same second optical axis into the irido-corneal angle of the eye is beneficial in that it enables direct application of the result of the evaluation of the condition into the treatment plan and surgery with precision in one clinical setting. Furthermore, combining OCT imaging and laser treatment allows targeting the ocular tissue with precision not available with any existing surgical systems and methods. Surgical precision afforded by the integrated surgical system allows for the affecting of only the targeted tissue of microscopic size and leaves the surrounding tissue intact. The microscopic size scale of the affected ocular tissue to be treated in the irido-corneal angle of the eye ranges from a few micrometers to a few hundred micrometers. For example, with reference to FIGS. 2 and 3 , the cross-sectional size of the normal Schlemm's canal 18 is an oval shape of a few tens of micrometers by a few hundred micrometers. The diameter of collector channels 19 and veins is a few tens of micrometers. The thickness of the juxtacanalicular tissue 17 is a few micrometers, the thickness of the trabecular meshwork 12 is around a hundred micrometers.

The control system of the integrated surgical system is further configured to instruct the laser source to modify a volume of ocular tissue within the outflow pathway to reduce a pathway resistance present in one or more of the trabecular meshwork, the Schlemm's canal, and the one or more collector channels by applying the laser beam to ocular tissue defining the volume to thereby cause photo-disruptive interaction with the ocular tissue to reduce the pathway resistance or create a new outflow pathway.

The laser source may be a femtosecond laser. Femtosecond lasers provide non-thermal photo-disruption interaction with ocular tissue to avoid thermal damage to surrounding tissue. Further, unlike other surgical methods, with femtosecond laser treatment opening surface incisions penetrating the eye can be avoided, enabling a non-invasive treatment. Instead of performing the treatment in a sterile surgical room, the non-invasive treatment can be performed in a non-sterile outpatient facility.

An additional imaging component may be included the integrated surgical system to provide direct visual observation of the irido-corneal angle along an angle of visual observation. For example, a microscope or imaging camera may be included to assist the surgeon in the process of docking the eye to the patient interface or an immobilizing device, location of ocular tissues in the eye and observing the progress of the surgery. The angle of visual observation can also be along the angled beam path 30 to the irido-corneal angle 13 through the cornea 3 and the anterior chamber 7.

Images from the OCT imaging apparatus and the additional imaging component providing visual observation, e.g. microscope, are combined on a display device such as a computer monitor. Different images can be registered and overlaid on a single window, enhanced, processed, differentiated by false color for easier understanding. Certain features are computationally recognized by a computer processor, image recognition and segmentation algorithm can be enhanced, highlighted, marked for display. The geometry of the treatment plan can also be combined and registered with imaging information on the display device and marked up with geometrical, numerical and textual information. The same display can also be used for user input of numerical, textual and geometrical nature for selecting, highlighting and marking features, inputting location information for surgical targeting by keyboard, mouse, cursor, touchscreen, audio or other user interface devices.

OCT Imaging

The main imaging component of the integrated surgical system disclosed herein is an OCT imaging apparatus. OCT technology may be used to diagnose, locate and guide laser surgery directed to the irido-corneal angle of the eye. For example, with reference to FIGS. 1-3 , OCT imaging may be used to determine the structural and geometrical conditions of the anterior chamber 7, to assess possible obstruction of the trabecular outflow pathway 40 and to determine the accessibility of the ocular tissue for treatment. As previously described, the iris 9 in a collapsed anterior chamber 7 may obstruct and close off the flow of aqueous humor 8, resulting in closed-angle glaucoma. In open-angle glaucoma, where the macroscopic geometry of the angle is normal, the permeability of ocular tissue may be affected, by blockage of tissue along the trabecular outflow pathway 40 or by the collapse of the Schlemm's canal 18 or collector channels 19.

OCT imaging can provide the necessary spatial resolution, tissue penetration and contrast to resolve microscopic details of ocular tissue. When scanned, OCT imaging can provide two-dimensional (2D) cross-sectional images of the ocular tissue. As another aspect of the integrated surgical system, 2D cross-sectional images may be processed and analyzed to determine the size, shape and location of structures in the eye for surgical targeting. It is also possible to reconstruct three-dimensional (3D) images from a multitude of 2D cross-sectional images but often it is not necessary. Acquiring, analyzing and displaying 2D images is faster and can still provide all information necessary for precise surgical targeting.

OCT is an imaging modality capable of providing high resolution images of materials and tissue. Imaging is based on reconstructing spatial information of the sample from spectral information of scattered light from within the sample. Spectral information is extracted by using an interferometric method to compare the spectrum of light entering the sample with the spectrum of light scattered from the sample. Spectral information along the direction that light is propagating within the sample is then converted to spatial information along the same axis via the Fourier transform. Information lateral to the OCT beam propagation is usually collected by scanning the beam laterally and repeated axial probing during the scan. 2D and 3D images of the samples can be acquired this way. Image acquisition is faster when the interferometer is not mechanically scanned in a time domain OCT, but interference from a broad spectrum of light is recorded simultaneously, this implementation is called a spectral domain OCT. Faster image acquisition may also be obtained by scanning the wavelength of light rapidly from a wavelength scanning laser in an arrangement called a swept-source OCT.

The axial spatial resolution limit of the OCT is inversely proportional to the bandwidth of the probing light used. Both spectral domain and swept source OCTs are capable of axial spatial resolution below 5 micrometers (m) with sufficiently broad bandwidth of 100 nanometers (nm) or more. In the spectral domain OCT, the spectral interference pattern is recorded simultaneously on a multichannel detector, such as a charge coupled device (CCD) or complementary metal oxide semiconductor (CMOS) camera, while in the swept source OCT the interference pattern is recorded in sequential time steps with a fast optical detector and electronic digitizer. There is some acquisition speed advantage of the swept source OCT but both types of systems are evolving and improving rapidly, and resolution and speed is sufficient for purposes of the integrated surgical system disclosed herein. Stand-alone OCT systems and OEM components are now commercially available from multiple vendors, such as Optovue Inc., Fremont, Calif., Topcon Medical Systems, Oakland, N.J., Carl Zeiss Meditec AG, Germany, Nidek, Aichi, Japan, Thorlabs, Newton, N.J., Santec, Aichi, Japan, Axsun, Billercia, Mass., and other vendors.

Femtosecond Laser Source

The preferred surgical component of the integrated surgical system disclosed herein is a femtosecond laser. A femtosecond laser provides highly localized, non-thermal photo-disruptive laser-tissue interaction with minimal collateral damage to surrounding ocular tissue. Photo-disruptive interaction of the laser is utilized in optically transparent tissue. The principal mechanism of laser energy deposition into the ocular tissue is not by absorption but by a highly nonlinear multiphoton process. This process is effective only at the focus of the pulsed laser where the peak intensity is high. Regions where the beam is traversed but not at the focus are not affected by the laser. Therefore, the interaction region with the ocular tissue is highly localized both transversally and axially along the laser beam. The process can also be used in weakly absorbing or weakly scattering tissue. While femtosecond lasers with photo-disruptive interactions have been successfully used in ophthalmic surgical systems and commercialized in other ophthalmic laser procedures, none have been used in an integrated surgical system that accesses the irido-corneal angle.

In known refractive procedures, femtosecond lasers are used to create corneal flaps, pockets, tunnels, arcuate incisions, lenticule shaped incisions, partial or fully penetrating corneal incisions for keratoplasty. For cataract procedures the laser creates a circular cut on the capsular bag of the eye for capsulotomy and incisions of various patterns in the lens for braking up the interior of the crystalline lens to smaller fragments to facilitate extraction. Entry incisions through the cornea opens the eye for access with manual surgical devices and for insertions of phaco emulsification devices and intra-ocular lens insertion devices. Several companies have commercialized such surgical systems, among them the Intralase system now available from Johnson & Johnson Vision, Santa Ana, Calif., The LenSx and Wavelight systems from Alcon, Fort Worth, Tex., other surgical systems from Bausch and Lomb, Rochester, N.Y., Carl Zeiss Meditec AG, Germany, Ziemer, Port, Switzerland, and LensAR, Orlando, Fla.

These existing systems are developed for their specific applications, for surgery in the cornea, and the crystalline lens and its capsular bag and are not capable of performing surgery in the irido-corneal angle 13 for several reasons. First, the irido-corneal angle 13 is not accessible with these surgical laser systems because the irido-corneal angle is too far out in the periphery and is outside of surgical range of these systems. Second, the angle of the laser beam from these systems, which is along the optical axis 24 to the eye, is not appropriate to reaching the irido-corneal angle 13, where there is significant scattering and optical distortion at the applied wavelength. Third, any imaging capabilities these systems may have do not have the accessibility, penetration depth and resolution to image the tissue along the trabecular outflow pathway 40 with sufficient detail and contrast.

In accordance with the integrated surgical system disclosed herein, clear access to the irido-corneal angle 13 is provided along the angled beam path 30. The tissue, e.g., cornea 3 and the aqueous humor 8 in the anterior chamber 7, along this angled beam path 30 is transparent for wavelengths from approximately 400 nm to 2500 nm and femtosecond lasers operating in this region can be used. Such mode locked lasers work at their fundamental wavelength with Titanium, Neodymium or Ytterbium active material. Non-linear frequency conversion techniques known in the art, frequency doubling, tripling, sum and difference frequency mixing techniques, optical parametric conversion can convert the fundamental wavelength of these lasers to practically any wavelength in the above mentioned transparent wavelength range of the cornea.

Existing ophthalmic surgical systems apply lasers with pulse durations longer than 1 ns have higher photo-disruption threshold energy, require higher pulse energy and the dimension of the photo-disruptive interaction region is larger, resulting in loss of precision of the surgical treatment. When treating the irido-corneal angle 13, however, higher surgical precision is required. To this end, the integrated surgical system may be configured to apply lasers with pulse durations from 10 femtosecond (fs) to 1 nanosecond (ns) for generating photo-disruptive interaction of the laser beam with ocular tissue in the irido-corneal angle 13. While lasers with pulse durations shorter than 10 fs are available, such laser sources are more complex and more expensive. Lasers with the described desirable characteristics, e.g., pulse durations from 10 femtosecond (fs) to 1 nanosecond (ns), are commercially available from multiple vendors, such as Newport, Irvine, Calif., Coherent, Santa Clara, Calif., Amplitude Systems, Pessac, France, NKT Photonics, Birkerod, Denmark, and other vendors.

Accessing the Irido-Corneal Angle

An important feature afforded by the integrated surgical system is access to the targeted ocular tissue in the irido-corneal angle 13. With reference to FIG. 6 , the irido-corneal angle 13 of the eye may be accessed via the integrated surgical system along an angled beam path 30 passing through the cornea 3 and through the aqueous humor 8 in the anterior chamber 7. For example, one or more of an imaging beam, e.g., an OCT beam and/or a visual observation beam, and a laser beam may access the irido-corneal angle 13 of the eye along the angled beam path 30.

An optical system disclosed herein is configured to direct a light beam to an irido-corneal angle 13 of an eye along an angled beam path 30. The optical system includes a first optical subsystem and a second optical subsystem. The first optical subsystem includes a window formed of a material with a refractive index n_(w) and has opposed concave and convex surfaces. The first optical subsystem also includes an exit lens formed of a material having a refractive index n_(x). The exit lens also has opposed concave and convex surfaces. The concave surface of the exit lens is configured to couple to the convex surface of the window to define a first optical axis extending through the window and the exit lens. The concave surface of the window is configured to detachably couple to a cornea of the eye with a refractive index n_(c) such that, when coupled to the eye, the first optical axis is generally aligned with the direction of view of the eye.

The second optical subsystem is configured to output a light beam, e.g., an OCT beam or a laser beam. The optical system is configured so that the light beam is directed to be incident at the convex surface of the exit lens along a second optical axis at an angle α that is offset from the first optical axis. The respective geometries and respective refractive indices n_(x), and n_(w) of the exit lens and window are configured to compensate for refraction and distortion of the light beam by bending the light beam so that it is directed through the cornea 3 of the eye toward the irido-corneal angle 13. More specifically, the first optical system bends the light beam to that the light beam exits the first optical subsystem and enters the cornea 3 at an appropriate angle so that the light beam progresses through the cornea and the aqueous humor 8 in a direction along the angled beam path 30 toward the irido-corneal angle 13.

Accessing the irido-corneal angle 13 along the angled beam path 30 provides several advantages. An advantage of this angled beam path 30 to the irido-corneal angle 13 is that the OCT beam and laser beam passes through mostly clear tissue, e.g., the cornea 3 and the aqueous humor 8 in the anterior chamber 7. Thus, scattering of these beams by tissue is not significant. With respect to OCT imaging, this enables the use of shorter wavelength, less than approximately 1 micrometer, for the OCT to achieve higher spatial resolution. An additional advantage of the angled beam path 30 to the irido-corneal angle 13 through the cornea 3 and the anterior chamber 7 is the avoidance of direct laser beam or OCT beam light illuminating the retina 11. As a result, higher average power laser light and OCT light can be used for imaging and surgery, resulting in faster procedures and less tissue movement during the procedure.

Another important feature provided by the integrated surgical system is access to the targeted ocular tissue in the irido-corneal angle 13 in a way that reduces beam discontinuity. To this end, the window and exit lens components of the first optical subsystem are configured to reduce the discontinuity of the optical refractive index between the cornea 3 and the neighboring material and facilitate entering light through the cornea at a steep angle.

Having thus generally described the integrated surgical system and some of its features and advantages, a more detailed description of the system and its component parts follows.

Integrated Surgical System

With reference to FIG. 7 , an integrated surgical system 1000 for non-invasive glaucoma surgery includes a control system 100, a surgical component 200, a first imaging component 300 and an optional second imaging component 400. In the embodiment of FIG. 7 , the surgical component 200 is a femtosecond laser source, the first imaging component 300 is an OCT imaging apparatus, and the optional second imaging component 400 is a visual observation apparatus, e.g., a microscope, for direct viewing or viewing with a camera. Other components of the integrated surgical system 1000 include beam conditioners and scanners 500, beam combiners 600, a focusing objective 700, and a patient interface 800.

The control system 100 may be a single computer or and plurality of interconnected computers configured to control the hardware and software components of the other components of the integrated surgical system 1000. A user interface 110 of the control system 100 accepts instructions from a user and displays information for observation by the user. Input information and commands from the user include but are not limited to system commands, motion controls for docking the patient's eye to the system, selection of pre-programmed or live generated surgical plans, navigating through menu choices, setting of surgical parameters, responses to system messages, determining and acceptance of surgical plans and commands to execute the surgical plan. Outputs from the system towards the user includes but are not limited to display of system parameters and messages, display of images of the eye, graphical, numerical and textual display of the surgical plan and the progress of the surgery.

The control system 100 is connected to the other components 200, 300, 400, 500 of the integrated surgical system 1000. Control signals from the control system 100 to the femtosecond laser source 200 function to control internal and external operation parameters of the laser source, including for example, power, repetition rate and beam shutter. Control signals from the control system 100 to the OCT imaging apparatus 300 function to control OCT beam scanning parameters, and the acquiring, analyzing and displaying of OCT images.

Laser beams 201 from the femtosecond laser source 200 and OCT beams 301 from the OCT imaging apparatus 300 are directed towards a unit of beam conditioners and scanners 500. Different kind of scanners can be used for the purpose of scanning the laser beam 201 and the OCT beam 301. For scanning transversal to a beam 201, 301, angular scanning galvanometer scanners are available for example from Cambridge Technology, Bedford, Mass., Scanlab, Munich, Germany. To optimize scanning speed, the scanner mirrors are typically sized to the smallest size, which still support the required scanning angles and numerical apertures of the beams at the target locations. The ideal beam size at the scanners is typically different from the beam size of the laser beam 201 or the OCT beam 301, and different from what is needed at the entrance of a focusing objective 700. Therefore, beam conditioners are applied before, after or in between individual scanners. The beam conditioner and scanners 500 includes scanners for scanning the beam transversally and axially. Axial scanning changes the depth of the focus at the target region. Axial scanning can be performed by moving a lens axially in the beam path with a servo or stepper motor.

The laser beam 201 and the OCT beam 301 are combined with dichroic, polarization or other kind of beam combiners 600 to reach a common target volume or surgical volume in the eye. In an integrated surgical system 1000 having a femtosecond laser source 200, an OCT imaging apparatus 300, and a visual observation device 400, the individual beams 201, 301, 401 for each of these components may be individually optimized and may be collinear or non-collinear to one another. The beam combiner 600 uses dichroic or polarization beam splitters to split and recombine light with different wavelength and/or polarization. The beam combiner 600 may also include optics to change certain parameters of the individual beams 201, 301, 401 such as beam size, beam angle and divergence. Integrated visual illumination, observation or imaging devices assist the surgeon in docking the eye to the system and identifying surgical locations.

To resolve ocular tissue structures of the eye in sufficient detail, the imaging components 300, 400 of the integrated surgical system 1000 may provide an OCT beam and a visual observation beam having a spatial resolution of several micrometers. The resolution of the OCT beam is the spatial dimension of the smallest feature that can be recognized in the OCT image. It is determined mostly by the wavelength and the spectral bandwidth of the OCT source, the quality of the optics delivering the OCT beam to the target location in the eye, the numerical aperture of the OCT beam and the spatial resolution of the OCT imaging apparatus at the target location. In one embodiment, the OCT beam of the integrated surgical system has a resolution of no more than 5 μm.

Likewise, the surgical laser beam provided by the femtosecond laser source 200 may be delivered to targeted locations with several micrometer accuracy. The resolution of the laser beam is the spatial dimension of the smallest feature at the target location that can be modified by the laser beam without significantly affecting surrounding ocular tissue. It is determined mostly by the wavelength of the laser beam, the quality of the optics delivering the laser beam to target location in the eye, the numerical aperture of the laser beam, the energy of the laser pulses in the laser beam and the spatial resolution of the laser scanning system at the target location. In addition, to minimize the threshold energy of the laser for photo-disruptive interaction, the size of the laser spot should be no more than approximately 5 μm.

It should be noted that, while the visual observation beam 401 is acquired by the visual observation device 400 using fixed, non-scanning optics, the OCT beam 301 of the OCT imaging apparatus 300 is scanned laterally in two transversal directions. The laser beam 201 of the femtosecond laser source 200 is scanned in two lateral dimensions and the depth of the focus is scanned axially.

For practical embodiments, beam conditioning, scanning and combining the optical paths are certain functions performed on the laser, OCT and visual observation optical beams. Implementation of those functions may happen in a different order than what is indicated in FIG. 7 . Specific optical hardware that manipulates the beams to implement those functions can have multiple arrangements with regards to how the optical hardware is arranged. They can be arranged in a way that they manipulate individual optical beams separately, in another embodiment one component may combine functions and manipulates different beams. For example, a single set of scanners can scan both the laser beam 201 and the OCT beam 301. In this case, separate beam conditioners set the beam parameters for the laser beam 201 and the OCT beam 301, then a beam combiner combines the two beams for a single set of scanners to scan the beams. While many combinations of optical hardware arrangements are possible for the integrated surgical system, the following section describes in detail an example arrangement.

Beam Delivery

In the following description, the term beam may—depending on the context—refer to one of a laser beam, an OCT beam, or a visual observation beam. A combined beam refers to two or more of a laser beam, an OCT beam, or a visual observation beam that are either collinearly combined or non-collinearly combined. Example combined beams include a combined OCT/laser beam, which is a collinear or non-colinear combination of an OCT beam and a laser beam, and a combined OCT/laser/visual beam, which is a collinear or non-collinear combination of an OCT beam, a laser beam, and a visual beam. In a collinearly combined beam, the different beams may be combined by dichroic or polarization beam splitters, and delivered along a same optical path through a multiplexed delivery of the different beams. In a non-collinear combined beam, the different beams are delivered at the same time along different optical paths that are separated spatially or by an angle between them. In the description to follow, any of the foregoing beams or combined beams may be generically referred to as a light beam. The terms distal and proximal may be used to designate the direction of travel of a beam, or the physical location of components relative to each other within the integrated surgical system. The distal direction refers to a direction toward the eye; thus an OCT beam output by the OCT imaging apparatus moves in the distal direction toward the eye. The proximal direction refers to a direction away from the eye; thus an OCT return beam from the eye moves in the proximal direction toward the OCT imaging apparatus.

Referring to FIG. 8 , an example integrated surgical system is configured to deliver each of a laser beam 201 and an OCT beam 301 in the distal direction toward an eye 1, and receive each of an OCT return beam and the visual observation beam 401 back from the eye 1. Regarding the delivery of a laser beam, a laser beam 201 output by the femtosecond laser source 200 passes through a beam conditioner 510 where the basic beam parameters, beam size, divergence are set. The beam conditioner 510 may also include additional functions, setting the beam power or pulse energy and shutter the beam to turn it on or off. After existing the beam conditioner 510, the laser beam 210 enters an axial scanning lens 520. The axial scanning lens 520, which may include a single lens or a group of lenses, is movable in the axial direction 522 by a servo motor, stepper motor or other control mechanism. Movement of the axial scanning lens 520 in the axial direction 522 changes the axial distance of the focus of the laser beam 210 at a focal point.

In accordance with a particular embodiment of the integrated surgical system, an intermediate focal point 722 is set to fall within, and is scannable in, the conjugate surgical volume 721, which is an image conjugate of the surgical volume 720, determined by the focusing objective 700. The surgical volume 720 is the spatial extent of the region of interest within the eye where imaging and surgery is performed. For glaucoma surgery, the surgical volume 720 is the vicinity of the irido-corneal angle 13 of the eye.

A pair of transverse scanning mirrors 530, 532 rotated by a galvanometer scanner scan the laser beam 201 in two essentially orthogonal transversal directions, e.g., in the x and y directions. Then the laser beam 201 is directed towards a dichroic or polarization beam splitter 540 where it is reflected toward a beam combining mirror 601 configured to combine the laser beam 201 with an OCT beam 301.

Regarding delivery of an OCT beam, an OCT beam 301 output by the OCT imaging apparatus 300 passes through a beam conditioner 511, an axially moveable focusing lens 521 and a transversal scanner with scanning mirrors 531 and 533. The focusing lens 521 is used set the focal position of the OCT beam in the conjugate surgical volume 721 and the real surgical volume 720. The focusing lens 521 is not scanned for obtaining an OCT axial scan. Axial spatial information of the OCT image is obtained by Fourier transforming the spectrum of the interferometrically recombined OCT return beam 301 and reference beams 302. However, the focusing lens 521 can be used to re-adjust the focus when the surgical volume 720 is divided into several axial segments. This way the optimal imaging spatial resolution of the OCT image can be extended beyond the Rayleigh range of the OCT signal beam, at the expense of time spent on scanning at multiple ranges.

Proceeding in the distal direction toward the eye 1, after the scanning mirrors 531 and 533, the OCT beam 301 is combined with the laser beam 201 by the beam combiner mirror 601. The OCT beam 301 and laser beam 201 components of the combined laser/OCT beam 550 are multiplexed and travel in the same direction to be focused at an intermediate focal point 722 within the conjugate surgical volume 721. After having been focused in the conjugate surgical volume 721, the combined laser/OCT beam 550 propagates to a second beam combining mirror 602 where it is combined with a visual observation beam 401 to form a combined laser/OCT/visual beam 701.

The combined laser/OCT/visual beam 701 traveling in the distal direction then passes through the focusing objective 700, and a window 801 of a patient interface, where the intermediate focal point 722 of the laser beam within the conjugate surgical volume 721 is re-imaged into a focal point in the surgical volume 720. The focusing objective 700 re-images the intermediate focal point 722, through the window 801 of a patient interface, into the ocular tissue within the surgical volume 720.

A scattered OCT return beam 301 from the ocular tissue travels in the proximal direction to return to the OCT imaging apparatus 300 along the same paths just described, in reverse order. The reference beam 302 of the OCT imaging apparatus 300, passes through a reference delay optical path and return to the OCT imaging apparatus from a moveable mirror 330. The reference beam 302 is combined interferometrically with the OCT return beam 301 on its return within the OCT imaging apparatus 300. The amount of delay in the reference delay optical path is adjustable by moving the moveable mirror 330 to equalize the optical paths of the OCT return beam 301 and the reference beam 302. For best axial OCT resolution, the OCT return beam 301 and the reference beam 302 are also dispersion compensated to equalize the group velocity dispersion within the two arms of the OCT interferometer.

When the combined laser/OCT/visual beam 701 is delivered through the cornea 3 and the anterior chamber 7, the combined beam passes through posterior and anterior surface of the cornea at a steep angle, far from normal incidence. These surfaces in the path of the combined laser/OCT/visual beam 701 create excessive astigmatism and coma aberrations that need to be compensated for.

With reference to FIGS. 9 a and 9 b , in an embodiment of the integrated surgical system 1000, optical components of the focusing objective 700 and patient interface 800 are configured to minimize spatial and chromatic aberrations and spatial and chromatic distortions. FIG. 9 a shows a configuration when both the eye 1, the patient interface 800 and the focusing objective 700 all coupled together. FIG. 9 b shows a configuration when both the eye 1, the patient interface 800 and the focusing objective 700 all detached from one another.

The patient interface 800 optically and physically couples the eye 1 to the focusing objective 700, which in turn optically couples with other optic components of the integrated surgical system 1000. The patient interface 800 serves multiple functions. It immobilizes the eye relative to components of the integrated surgical system; creates a sterile barrier between the components and the patient; and provides optical access between the eye and the instrument. The patient interface 800 is a sterile, single use disposable device and it is coupled detachably to the eye 1 and to the focusing objective 700 of the integrated surgical system 1000.

The patient interface 800 includes a window 801 having an eye-facing, concave surface 812 and an objective-facing, convex surface 813 opposite the concave surface. The window 801 thus has a meniscus form. With reference to FIG. 9 c , the concave surface 812 is characterized by a radius of curvature r_(e), while the convex surface 813 is characterized by a radius of curvature r_(w). The concave surface 812 is configured to couple to the eye, either through a direct contact or through index matching material, liquid or gel, placed in between the concave surface 812 and the eye 1. The window 801 may be formed of glass and has a refractive index n_(w). In one embodiment, the window 801 is formed of fused silica and has a refractive index n_(w) of 1.45. Fused silica has the lowest index from common inexpensive glasses. Fluoropolymers such as the Teflon AF are another class of low index materials that have refractive indices lower than fused silica, but their optical quality is inferior to glasses and they are relatively expensive for high volume production. In another embodiment the window 801 is formed of the common glass BK7 and has a refractive index n_(w) of 1.50. A radiation resistant version of this glass, BK7G18 from Schott AG, Mainz, Germany, allows gamma sterilization of the patient interface 800 without the gamma radiation altering the optical properties of the window 801.

Returning to FIGS. 9 a and 9 b , the window 801 is surrounded by a wall 803 of the patient interface 800 and an immobilization device, such as a suction ring 804. When the suction ring 804 is in contact with the eye 1, an annular cavity 805 is formed between the suction ring and the eye. When vacuum applied to the suction ring 804 and the cavity via a vacuum tube a vacuum pump (not shown in FIGS. 9 a and 9 b ), vacuum forces between the eye and the suction ring attach the eye to the patient interface 800 during surgery. Removing the vacuum releases or detach the eye 1.

The end of the patient interface 800 opposite the eye 1 includes an attachment interface 806 configured to attach to the housing 702 of the focusing objective 700 to thereby affix the position of the eye relative to the other components of the integrated surgical system 1000. The attachment interface 806 can work with mechanical, vacuum, magnetic or other principles and it is also detachable from the integrated surgical system.

The focusing objective 700 includes an aspheric exit lens 710 having an eye-facing, concave surface 711 and a convex surface 712 opposite the concave surface. The exit lens 710 thus has a meniscus form. While the exit lens 710 shown in FIGS. 9 a and 9 b is an aspheric lens giving more design freedom, in other configurations the exit lens may be a spherical lens. Alternatively, constructing the exit lens 710 as a compound lens, as opposed to a singlet, allows more design freedom to optimize the optics while preserving the main characteristics of the optical system as presented here. With reference to FIG. 9 c , the concave surface 711 is characterized by a radius of curvature r_(y), while the convex surface 712 is characterized by an aspheric shape. The aspheric convex surface 712 in combination with the spherical concave surface 711 result in an exit lens 710 having varying thickness, with the outer perimeter edges 715 of the lens being thinner than the central, apex region 717 of the lens. The concave surface 711 is configured to couple to the convex surface 813 of the window 801. In one embodiment, the exit lens 710 is formed of fused silica and has a refractive index n_(x) of 1.45.

FIGS. 10 a and 10 b are schematic illustrations of components of the integrated surgical system of FIGS. 7 and 8 functionally arranged to form an optical system 1010 having a first optical subsystem 1001 and a second optical subsystem 1002 that enable access to a surgical volume 720 in the irido-corneal angle. Each of FIGS. 10 a and 10 b include components of the focusing objective 700 and the patient interface 800 of FIG. 9 a . However, for simplicity, the entirety of the focusing objective and the patient interface are not included in FIGS. 10 a and 10 b . Also, for additional simplicity in FIG. 10 a , the planar beam-folding mirror 740 of FIGS. 9 a and 9 b is not included and the combined laser/OCT/visual beam 701 shown in FIG. 9 a is unfolded or straightened out. It is understood by those skilled in the art that adding or removing planar beam folding mirrors does not alter the principal working of the optical system formed by the first optical subsystem and the second optical subsystem. FIG. 10 c is a schematic illustration of a beam passing through the first optical subsystem of FIGS. 10 a and 10 b.

With reference to FIG. 10 a , a first optical subsystem 1001 of the integrated surgical system 1000 includes the exit lens 710 of a focusing objective 700 and the window 801 of a patient interface 800. The exit lens 710 and the window 801 are arranged relative to each other to define a first optical axis 705. The first optical subsystem 1001 is configured to receive a beam, e.g., a combined laser/OCT/visual beam 701, incident at the convex surface 712 of the exit lens 710 along a second optical axis 706, and to direct the beam toward a surgical volume 720 in the irido-corneal angle 13 of the eye.

During a surgical procedure, the first optical subsystem 1001 may be assembled by interfacing the convex surface 813 of the window 801 with the concave surface 711 of the exit lens 710. To this end, a focusing objective 700 is docked together with a patient interface 800. As a result, the concave surface 711 of the exit lens 710 is coupled to the convex surface 813 of the window 801. The coupling may be by direct contact or through a layer of index matching fluid. For example, when docking the patient interface 800 to focusing objective 700, a drop of index matching fluid can be applied between the contacting surfaces to eliminate any air gap that may be between the two surfaces 711, 813 to thereby help pass the combined laser/OCT/visual beam 701 through the gap with minimal Fresnel reflection and distortion.

In order to direct the beam toward the surgical volume 720 in the irido-corneal angle 13 of the eye, the first optical subsystem 1001 is designed to account for refraction of the beam 701 as it passes through the exit lens 710, the window 801 and the cornea 3. To this end, and with reference to FIG. 10 c , the refractive index n_(x) of the exit lens 710 and the refractive index n_(w) of the window 801 are selected in view of the refractive index n_(c) of the cornea 3 to cause appropriate beam bending through the first optical subsystem 1001 so that when the beam 701 exits the subsystem and passes through the cornea 3, the beam path is generally aligned to fall within the irido-corneal angle 13.

Continuing with reference to FIG. 10 c and beginning with the interface between the window 801 and the cornea 3. Too steep of an angle of incidence at the interface where the combined laser/OCT/visual beam 701 exits the window 801 and enters the cornea 3, i.e., at the interface between the concave surface 812 of the window and the convex surface of the cornea 3, can create excessive refraction and distortion. To minimize refraction and distortion at this interface, in one embodiment of the first optical subsystem 1001, the refractive index of the window 801 is closely matched to the index of the cornea 3. For example, as describe above with reference to FIGS. 9 a and 9 b , the window 801 may have a refractive index lower than 1.42 to closely match the cornea 3, which has a refractive index of 1.36.

Excessive refraction and distortion at the interface where the combined laser/OCT/visual beam 701 exits the window 801 and enters the cornea 3 may be further compensated for by controlling the bending of the beam 701 as it passed through the exit lens 710 and the window 801. To this end, in one embodiment of the first optical subsystem 1001 the index of refraction n_(w) of the window 801 is larger than each of the index of refraction n_(x) of the exit lens 710 and the index of refraction n_(c) of the cornea 3. As a result, at the interface where the combined laser/OCT/visual beam 701 exits the exit lens 710 and enters the window 801, i.e., interface between the concave surface 711 of the exit lens and the convex surface 813 of the window, the beam passes through a refractive index change from high to low that cause the beam to bend in a first direction. Then, at the interface where the combined laser/OCT/visual beam 701 exits the window 801 and enters the cornea 3, i.e., interface between the concave surface 812 of the exit lens and the convex surface of the cornea, the beam passes through a refractive index change from low to high that cause the beam to bend in a second direction opposite the first direction.

The shape of the window 801 is chosen to be a meniscus lens. As such, the incidence angle of light has similar values on both surfaces 812, 813 of the window 801. The overall effect is that at the convex surface 813 the light bends away from the surface normal and at the concave surface 812 the light bends towards the surface normal. The effect is like when light passes through a plan parallel plate. Refraction on one surface of the plate is compensated by refraction on the other surface a light passing through the plate does not change its direction. Refraction at the entering, convex surface 712 of the exit lens 710 distal to the eye is minimized by setting the curvature of the entering surface such that angle of incidence β of light 701 at the entering surface is close to a surface normal 707 to the entering surface at the intersection point 708.

Here, the exit lens 710, the window 801, and the eye 1 are arranged as an axially symmetric system with a first optical axis 705. In practice, axial symmetry is an approximation because of manufacturing and alignment inaccuracies of the optical components, the natural deviation from symmetry of the eye and the inaccuracy of the alignment of the eye relative to the window 801 and the exit lens 710 in a clinical setting. But, for design and practical purposes the eye 1, the window 801, and the exit lens 710 are considered as an axially symmetric first optical subsystem 1001.

With continued reference to FIG. 10 a , a second optical subsystem 1002 is optically coupled to the first optical subsystem 1001 at an angle α relative to the first optical axis 705 of the first optical subsystem 1001. The advantage of this arrangement is that both optical subsystems 1001, 1002 can be designed at a much lower numerical aperture compared to a system where all optical components are designed on axis with a common optical axis.

The second optical subsystem 1002 includes a relay lens 750 that, as previously described with reference to FIG. 8 , generates a conjugate surgical volume 721 of the surgical volume 720 within the eye. The second optical subsystem 1002 includes various other components collectively indicated as an optical subsystem step 1003. Referring to FIG. 8 , these components may include a femtosecond laser source 200, an OCT imaging apparatus 300, a visual observation device 400, beam conditioners and scanners 500, and beam combiners 600.

The second optical subsystem 1002 may include mechanical parts (not shown) configured to rotate the entire subsystem around the first optical axis 705 of the first optical subsystem 1001. This allows optical access to the whole 360-degree circumference of the irido-corneal angle 13 of the eye 1.

With reference to FIG. 10 b , flexibility in arranging the first and second optical subsystems 1001, 1002, relative to each other may be provided by an optical assembly 1004 interposed between the optical output of the second optical subsystem 1002 and the optical input of the first optical subsystem 1001. In one embodiment, the optical assembly 1004 may include one or more planar beam-folding mirrors 740, prisms (not shown) or optical gratings (not shown) configured to receive the optical output, e.g., combined laser/OCT/visual beam 701, of the second optical subsystem 1002, change or adjust the direction of the combined laser/OCT/visual beam, and direct the beam to the optical input of the first optical subsystem 1001 while preserving the angle α between the first optical axis 705 and the second optical axis 706.

In another configuration, the optical assembly 1004 of planar beam-folding mirrors 740 further includes mechanical parts (not shown) configured to rotate the assembly around the first optical axis 705 of the first optical subsystem 1001 while keeping the second optical subsystem 1002 stationary. Accordingly, the second optical axis 706 of the second optical subsystem 1002 can be rotated around the first optical axis 705 of the first optical subsystem 1001. This allows optical access to the whole 360-degree circumference of the irido-corneal angle 13 of the eye 1.

With considerations described above with reference to FIGS. 9 a, 9 b and 9 c , the design of the first optical subsystem 1001 is optimized for angled optical access at an angle α relative to the first optical axis 705 of the first optical subsystem 1001. Optical access at the angle α compensates for optical aberrations of the first optical subsystem 1001. Table 1 shows the result of the optimization at access angle α=72 degrees with Zemax optical design software package. This design is a practical embodiment for image guided femtosecond glaucoma surgery.

TABLE 1 Center Structure and Refractive Radius Thickness Surface Material index [mm] [mm] concave Exit lens 710 of 1.45 −10 4.5 surface focusing objective. 711, convex Fused silica surface 712 concave Window 801 of 1.50 −10.9 1.0 surface patient interface. 812, convex BK7G18 surface 813 3 Cornea 1.36 −7.83 0.54 8 Aqueous humor 1.32 −6.53 3.5 Target Ophthalmic tissue 1.38 N/A 0 to 1 mm

This design produces diffraction limited focusing of 1030 nm wavelength laser beams and 850 nm wavelength OCT beams with numerical aperture (NA) up to 0.2. In one design, the optical aberrations of the first optical subsystem are compensated to a degree that the Strehl ratio of the first optical subsystem for a beam with numerical aperture larger than 0.15 at the irido-corneal angle is larger than 0.9. In another design, the optical aberrations of the first optical subsystem are partially compensated, the remaining uncompensated aberrations of the first optical system are compensated by the second optical subsystem to a degree that the Strehl ratio of the combined first and second optical subsystem for a beam with numerical aperture larger than 0.15 at the irido-corneal angle is larger than 0.9.

Calibration

The femtosecond laser source 200, OCT imaging apparatus 300, and visual observation device 400 of the integrated surgical system 1000 are first individually calibrated to ensure their internal integrity and then cross-calibrated for system integrity. The essential part of system calibration is to ensure that the when the surgical focus of a laser beam 201 is commanded to a location of a surgical volume 720, as identified by the OCT imaging apparatus and/or the visual observation device 400, the achieved location of the focus matches the commanded location of the focus within a certain tolerance, typically within 5 to 10 μm. Also, graphical and cursor outputs, images, overlays displayed on a user interface 110, such as a computer monitor, and user inputs of ocular tissue surgical volume 720 locations accepted from the user interface 110 should correspond to actual locations in tissue within predetermined tolerances of similar accuracy.

One embodiment of this spatial calibration procedure starts with imaging calibrated scales and scaling magnifications of the OCT imaging apparatus 300 and/or the visual observation device 400 and their displays in a way that the scale value on the display matches the real scale of the calibration target. Then laser calibration patters are exposed or burned into transparent calibration targets, and the calibration patterns are subsequently imaged. Then, the intended patterns and the actual burned patterns are compared with the imaging system of the integrated surgical system 1000 or by a separate microscope. If they do not match within the specified tolerance, the scaling parameters of the surgical patterns are re-scaled by adjusting the scaling of the laser beam scanners. This procedure is iterated, if necessary, until all spatial calibrations are within tolerance.

Laser Surgery with Ocular Tissue Modification

The anatomy of the eye relevant to the surgical treatment enabled by the integrated surgical system 1000 disclosed herein is illustrated in FIGS. 1-4 . To reduce the IOP, laser treatment targets ocular tissues that affect the trabecular outflow pathway 40. These ocular tissues may include the trabecular meshwork 12, the scleral spur 14, the uveal 15, the corneoscleral meshwork 16, the juxtacanalicular tissue 17, the Schlemm's canal 18, the collector channels 19 within the irido-corneal angle 13.

Disclosed herein is a laser pattern particularly effective in affecting the trabecular outflow pathway 40. Since the laser interaction volume is small, on the order of a few micrometers (μm), the interaction of ocular tissue with each laser shot of a repetitive laser breaks down ocular tissue locally at the focus of the laser. Pulse duration of the laser for photo-disruptive interaction in ocular tissue can range from several femtoseconds to several nanoseconds and pulse energies from several nanojoules to tens of microjoules. The laser pulses at the focus, through multiphoton processes, breaks down chemical bonds in the molecules, locally photo-dissociate tissue material and create gas bubbles in wet tissue. The breakdown of tissue material and mechanical stress from bubble formation fragments the tissue and create clean continuous cuts when the laser pulses are laid down in proximity to one another along geometrical lines and surfaces.

For the sake of the following description the basic interaction volumes are referred to as cells. The size of a cell is determined by the extent of the influence of the laser-tissue interaction. When the laser spots, or cells, are spaced close along a line, the laser creates a narrow, microscopic channel. A wider channel can be created by closely spacing a multitude of laser spots within the cross section of the channel. For example, a cylindrical channel can be created by first calculating the coordinates of the overall position and size of the cylinder. Then, using the size of the cells as a parameter, calculate the coordinates of each cell in a closely packed cell arrangement within the volume of the cylinder. The arrangement of the cells resembles the arrangement of atoms in a crystal structure.

The easiest is to calculate a cubic cell structure, in this case the individual cells are arranged in regularly spaced rows, columns and sheets, and the coordinates of the cells can be calculated sequentially from neighbor to neighbor in the order of rows columns and sheets. The laser scanner hardware can also follow this regular sequence to scan the laser beam without excessive jumps. Channels can be created with different cross sections, with oval, rectangular, square or other regular or irregular cross sections. A channel cut in the ocular tissue can conduct aqueous humor 8, its conductivity increasing with the cross-sectional area of the channel.

FIGS. 11 a and 11 b illustrate sectional views of the irido-corneal angle where the surgical laser scans to affect a surgical volume 900 (FIG. 11 a ) to form a channel opening 920 (FIG. 11 b ). The surgical volume 900 in the trabecular meshwork, extends from the anterior chamber 7 and through the inner wall of the Schlemm's canal 18. Laser scanning modifies the ocular tissue in the surgical volume 900 to create a channel opening 920. The channel opening 920 reduces the flow resistance in the ocular tissue to increase aqueous flow from the anterior chamber 7 into the Schlemm's canal 18 and thereby reduce the IOP of the eye. The size of the channel opening 920 will determine the reduction of the outflow pathway resistance and the longevity of effectiveness.

Image guidance is essential for this procedure to locate the structures precisely and to monitor the success of the treatment. Minimizing the size and volume of the treated ocular tissue also helps minimize the amount of gas created and gas-induced tissue movements. As the tissue expands with the expanding gas, sudden tissue movements can occur when gas escapes from a closed volume and the gas filled void collapses. Such sudden tissue movements can create discontinuities in the surgical incisions and should be avoided or minimized.

Another consideration for creating surgical patterns in the ocular tissue is the potential shadow effect of the gas bubbles as the incision progresses. In general, the incision progresses should proceed from a location further from the laser and progress towards a location closer to the laser to minimize the shadow effect. The amount of gas is also less when the laser is focused tightly to a diffraction limited focal spot and the threshold pulse energy for photo-disruption interaction is lowered. When the laser is operated at low threshold, the size of local interaction volume and the size of the gas bubbles are smaller. This means that the cells filling the surgical volume should be spaced closer.

Table 2 displays surgical laser and treatment pattern parameters for several incisions of different sizes. The range of the parameter set is limited by the Maximum Permissible Exposure (MPE) limit of laser light entering the eye and practical ranges for the repetition rate of the laser and the scanning speed of the scanners.

TABLE 2 Channel size Channel Cell size Laser Laser Laser x[mm], cross x[μm], average repetition pulse Procedure Tissue y[mm], section y[μm], power rate energy time treated z[mm] [mm²] z[μm] [W] [kHz] [μJ] [s] Trabecular 1.5, 0.2, 0.2 0.3 3, 3, 3 0.9 300 3 7.4 meshwork Trabecular   2, 0.2, 0.2 0.4 4, 4, 4 1 200 5 6.3 meshwork

With respect to MPE, the angled beam path 30 of FIG. 6 is the most advantageous since light beams from the femtosecond laser source 200 or the OCT imaging apparatus 300 transmitted through the tissue do not directly reach the retina. This is in contrast with known corneal and cataract surgeries, where direct laser light or OCT light transmitted through the tissue reaches the retina. Therefore, the angled beam path 30 of FIG. 6 can use higher beam average power. Higher average power for the surgical laser results in faster procedure time. Higher average power for the OCT beam results in faster OCT image acquisition time for the same image quality or better image quality for the same image acquisition time. With respect to cell size and laser pulse energy, smaller cell sizes and pulse energies are preferred to minimize the amount of gas created in the tissue.

Linear perfusion models, experimental (Liu et al., 2005) and clinical findings from ELT procedures indicate channel cross sections from 0.24 mm² to 0.4 mm² can achieve sufficient IOP reduction. As seen from Table 2, the surgical laser procedure enabled by the integrated surgical system disclosed herein can produce similar channel cross sections to those in Liu et al. and can be completed in less than 10 seconds.

FIG. 12 is a flowchart of a method of reducing intraocular pressure in an eye having a cornea, an anterior chamber, and an irido-corneal angle comprising an aqueous humor outflow pathway formed of a trabecular meshwork, a Schlemm's canal, and one or more collector channels branching from the Schlemm's canal, the method comprising. The method may be performed by the integrated surgical system 1000 of FIGS. 7-10 b.

At step 1202, an OCT beam 301 is delivered through the cornea 3 and the anterior chamber 7 into the irido-corneal angle 13. In one embodiment, the OCT beam 301 has a resolution less than or equal to approximately 5 micrometers and is delivered to the irido-corneal angle 13 by directing the OCT beam to a first optical subsystem 1001 that includes a window 801 coupled to the cornea 3 and an exit lens 710 coupled to the window.

At step 1204, an OCT image of a portion of the irido-corneal angle 13 is acquired based on the OCT beam 301 delivered to the irido-corneal angle through the first optical subsystem 1001. To this end, an OCT return beam 301 is received through the first optical subsystem 1001 and processed at an OCT imaging apparatus 300 using known OCT imaging techniques.

At step 1206, a surgical volume 900 of ocular tissue to be modified is determined based on the OCT image. The surgical volume 900 may be determined based on a 2D cross-sectional OCT image that is displayed on a control system 100 of the integrated surgical system 1000. A visual observation beam 401 may also be used to determine the surgical volume 900. To this end, a visual observation beam 401 may be acquired from the irido-corneal angle 13 by a microscope 400 through the first optical subsystem 1001, and the volume 900 of ocular tissue to modify may be determined by presenting the OCT image and visual observation signal overlaid on a display screen of the control system 100. Alternatively, the OCT image and visual observation signal may be registered on a display screen.

In one embodiment, the Schlemm's canal 18 is characterized by a circumference, and the surgical volume 900 of ocular tissue to modify is determined based on the density of collector channels 19 around the circumference. In this case, a density distribution of collector channels 19 around at least a portion of the circumference of the Schlemm's canal 18 is determined based on OCT images. A region of the Schlemm's canal 18 having a density above a threshold criterion is identified, and the proximity of the identified region is included in the volume of ocular tissue to modify. The criterion may be the 50^(th) percentile of the distribution, the 75^(th) percentile, or a numerical value higher than the 75^(th) percentile. In another embodiment, the volume 900 of ocular tissue to be modified is in the proximity of one or more of the collector channels 19.

At step 1208, each of an OCT beam 301 and a laser beam 201 is delivered through the cornea 3, and the anterior chamber 7 into the irido-corneal angle 13. In one embodiment, the OCT beam 301 and laser beam 201 have substantially equal resolutions, e.g., less than or equal to approximately 5 micrometers, and each beam is delivered to the irido-corneal angle by directing each beam to a first optical subsystem 1001 that includes a window 801 coupled to the cornea 3 and an exit lens 710 coupled to the window. The OCT beam 301 and the laser beam 201 may be collinearly directed to the first optical subsystem 1001 along a same optical path, for example by multiplexing the beams. Alternatively, the OCT beam 301 and the laser beam 201 may be non-collinearly directed to the first optical subsystem at the same time along spatially separated or angled optical paths.

Distortion and aberrations of the beams 201, 301 caused by oblique angle entry into the eye are compensated for by directing each beam into the first optical subsystem 1001 at an angle. To this end, the eye 1 includes a direction of view and the first optical subsystem 1001 is positioned relative to the eye so as to include a first optical axis 705 that is substantially aligned with the direction of view of the eye. The beams 201, 301 are input to the first optical subsystem 1001 by directing each beam into a convex surface 713 of the exit lens 710 along a second optical axis 706 offset from the first optical axis 705 by an angle α. Additionally, each beam 201, 301 may be directed into the convex surface 713 of the exit lens 710 at an angle β relative to a surface normal 707 to the convex surface.

At step 1210, a volume 900 of ocular tissue within the trabecular outflow pathway 40 is modified to reduce a pathway resistance present in one or more of the trabecular meshwork 12, the Schlemm's canal 18, and the one or more collector channels 19 by applying the laser beam 201 to ocular tissue defining the volume. To this end, a laser beam 201 having a wavelength between 330 nanometers and 2000 nanometers may be scanned in multiple directions to interact with the ocular tissue defining the surgical volume 900. The laser beam 201 may be applied in a continuous manner or as a multitude of laser pulses with a pulse duration between 20 femtoseconds and 1 nanosecond. The laser beam 201 causes photo-disruptive interaction with the ocular tissue to reduce the pathway resistance or create a new outflow pathway 40. In one embodiment, photo-disruptive interaction with the ocular tissue creates a channel opening 902 opened through the trabecular meshwork connecting the anterior chamber and the Schlemm's canal.

Accessing the Irido-Corneal Angle

FIG. 13 is a flowchart of a method of directing a light beam to an irido-corneal angle of an eye having a direction of view and a cornea with a refractive index n_(c). The method may be performed by the integrated surgical system 1000 of FIGS. 7-10 b.

At step 1302, a first optical subsystem 1001 and a second optical subsystem 1002 are arranged relative to each other. The first optical subsystem 1001 includes a window 801 formed of a material with a refractive index n_(w). The window 801 has a concave surface 812 and a convex surface 813 opposite the concave surface. The first optical subsystem 1001 also includes and an exit lens 710 formed of a material having a refractive index n_(x). The exit lens 710 has a concave surface 711 and a convex surface 712 opposite the concave surface. The concave surface 711 of the exit lens 710 is configured to couple to the convex surface 813 of the window 801 to define a first optical axis 705 extending through the window and the exit lens. The concave surface 812 of the window 801 is configured to detachably couple to the cornea 3 of the eye such that the first optical axis 705 is generally aligned with the direction of view of the eye.

At step 1304, a light beam output by the second optical subsystem 1002 is directed to be incident at the convex surface 712 of the exit lens 710 along a second optical axis 706 at an angle α that is offset from the first optical axis 705. To this end, the second optical subsystem 1002 or another intermediate optical assembly 1004 may be configured to determine a measure of angle separation between the first optical axis and the second optical axis, and to adjust the orientation of the second optical axis until the angle of separation is at angle α. The angle α is typically greater than 30 degrees. More specifically, the angle α may be between 60 degrees and 80 degrees. Even more specifically, the angle α is approximately 72 degrees.

At step 1306, the light beam output by the second optical subsystem 1002 may be also directed to intersect the convex surface 712 of the exit lens 710 at an intersection point and an angle δ between the second optical axis 706 and a surface normal 707 to the convex surface of the exit lens. Again, the second optical subsystem 1002 or another intermediate optical assembly 1004 may be configured to determine a measure of angle separation between the second optical axis and the surface normal 707, and to adjust the orientation of the second optical axis until the angle of separation is at angle β.

In some arrangements, as shown for example in FIG. 10 b , the second optical subsystem 1002 may be configured to be arrange relative to the first optical subsystem 1001 so that the light beam 701 is output by the second optical subsystem along an axis offset from the second optical axis 706. In these cases, in the directing process of step 1304, the light beam 701 is received at an optical assembly 1004 interposed between the first optical subsystem 1001 and the second optical subsystem 1002 and redirected into general alignment with the second optical axis 706. The second optical axis 706 may be rotated around the first optical axis 705 while maintaining the second optical axis offset from the first optical axis by an angle substantially equal to the angle α. Doing so allows for treatment around the circumference of the irido-corneal angle 13. In configurations where the second optical axis 706 intersects the convex surface 712 of the exit lens 710 at an intersection point 708 and at an angle β between the second optical axis and a surface normal 707 to the convex surface of the exit lens, the directing process of step 1306 involves rotating the second optical axis around the first optical axis while also maintaining an angle between the second optical axis and the surface normal that is substantially equal to the angle β.

Minimally Invasive and Non-Invasive Surgical Treatments

Surgical treatments disclosed below reduce outflow pathway resistance while minimizing ocular tissue modification through careful design and selection of laser treatment patterns. As used herein a treatment pattern defines a three-dimensional model of ocular tissue to be modified by a laser or a three-dimensional model of ocular fluid to be affected by a laser. A treatment pattern is typically defined by a set of surgical parameters. The surgical parameters may include one or more of a treatment area A that represents a surface area of ocular tissue through which the laser will travel and a treatment thickness t that represents the level to which the laser will cut into the ocular tissue or the level at which the laser will affect ocular fluid. Thus, a laser applied in accordance with a treatment pattern may affect or produce a surgical volume that resembles the three-dimensional model of the treatment pattern, or may affect fluid located in an interior of an eye structure resembled by the three-dimensional model.

Additional surgical parameters define the placement of the surgical volume or affected volume within the eye. Placement parameters may include one or more of a location l that represents where the treatment is to occur relative to the circumferential angle of the eye, and a treatment depth d that represents a position of the three-dimensional model of ocular tissue or ocular fluid within the eye relative to a reference eye structure. In the following, the treatment depth d is shown and described relative to the region where the anterior chamber 7 meets the trabecular meshwork 12. Together, the treatment pattern and the placement parameters define a treatment plan.

Minimizing or eliminating the invasiveness of the surgical treatment procedure is beneficial for multiple reasons. First, non-invasive treatments and minimally invasive treatments minimize damage to healthy ocular tissue and thereby preserve the filtering function of untreated parts of the trabecular meshwork tissue. Second, by preserving the mechanical structural integrity of the trabecular meshwork tissue as much as possible, the potential for the collapse and closure of the existing or newly created outflow pathway is minimized. Third, the disclosed laser treatment patterns give more control over the amount of IOP reduction. Achieving the right IOP is important for the clinical outcome. Too small of an IOP reduction diminishes the effectiveness of glaucoma treatment, while too large of an IOP reduction may cause deflation of the eye. Finally, minimizing the volume of laser treated ocular tissue results in faster procedure time and reduces the chance of unintended tissue movement during the procedure.

Minimally Invasive Laser Surgery

As described above, a femtosecond laser provides highly localized, non-thermal photo-disruptive laser-tissue interaction with minimal collateral damage to surrounding ocular tissue. Photo-disruptive interaction of the laser is utilized in optically transparent tissue. The principal mechanism of laser energy deposition into the ocular tissue is not by absorption but by a highly nonlinear multiphoton process. This process is effective only at the focus of the pulsed laser where the peak intensity is high. Regions where the beam is traversed but not at the focus are not affected by the laser. Therefore, the interaction region with the ocular tissue is highly localized both transversally and axially along the laser beam.

Applying the foregoing femtosecond laser capabilities, an embodiment of the integrated surgical system 1000, reduces outflow pathway resistance using one or more laser treatment patterns to modify ocular tissue in a localized manner. Referring to FIG. 3 , as previously described, the trabecular meshwork 12 has three layers, the uveal 15, the corneoscleral meshwork 16, and the juxtacanalicular tissue 17. These layers are porous and permeable to aqueous, with the uveal 15 being the most porous and permeable, followed by the corneoscleral meshwork 16. The least porous and least permeable layer of the trabecular meshwork 12 is the juxtacanalicular tissue 17. The inner wall 18 a of the Schlemm's canal 18, which is also porous and permeable to aqueous, has characteristics similar to the juxtacanalicular tissue 17. Based on this knowledge, various treatment patterns that 1) select one or more layers of the trabecular meshwork 12 for modification and 2) control the extent of such modifications, may be designed. These treatment patterns are defined by a set of surgical parameters, which in turn, define the geometrical dimensions of ocular tissue modifications (or surgical cuts) that result from laser surgery. Examples of different treatment patterns follow.

In one example, with reference to FIGS. 11 a, 11 b, and 11 c , which illustrate sectional views and a perspective view of the irido-corneal angle 13, a surgical laser 701 may scan ocular tissue in accordance with a first treatment pattern P1 designed to affect a surgical volume 900 (shown in two and three dimensions in FIG. 11 a ) to form a contiguous, wide and deep channel opening 920 (shown in two dimensions in FIG. 11 b and three dimensions in FIG. 11 c ). The deep channel opening 920 extends from the anterior chamber 7, through each of the uveal 15, the corneoscleral meshwork 16, the juxtacanalicular tissue 17 of the trabecular meshwork 12, and the inner wall 18 a of the Schlemm's canal 18. The deep channel opening, and other channel opening disclosed herein, may be a single lumen defining a fluid pathway or an arrangement of adjacent pores forming a sponge like structure defining a fluid pathway or a combination thereof.

The movement of the laser as it scans to affect the surgical volume 900 follows the first treatment pattern P1, which is defined by a set of surgical parameters that include a treatment area A and a thickness t. The treatment area A is defined by a width w and a height h. The width may be defined in terms of a measure around the circumferential angle. For example, the width w may be defined in terms of an angle, e.g., 90 degrees, around the circumferential angle.

An initial placement of the laser focus within the eye is defined by a set of placement parameters, including a depth d (not shown) and a location l (not shown). The location l defines a point around the circumferential angle of the eye at which laser treatment will begin, while the depth d defines a point between the anterior chamber 7 and the Schlemm's canal 18 where the treatment begins or ends.

The channel opening 920 (FIGS. 11 b and 11 c ) resulting from laser application of the first treatment pattern P1 resembles the surgical volume 900 and is characterized by an area A and thickness t similar to those of the surgical volume and the treatment pattern. The depth d is essentially null, thus placing an end of the surgical volume 900 at the region where the anterior chamber 7 meets the trabecular meshwork 12. The thickness t of the resulting deep channel opening 920 extends from the anterior chamber 7 and through the inner wall 18 a of the Schlemm's canal 18, while the area A is such that the resulting channel opening 920 (FIGS. 11 b and 11 c ) is characterized by a single opening.

In the example of FIGS. 11 b and 11 c , the channel opening 920 has a first end in fluid communication with the Schlemm's canal 18 and a second end in fluid communication with the anterior chamber 7. The fluid communication may be enabled through a one or more lumens forming a pathway through the channel opening 920 and/or an arrangement of pores forming a porous pathway through the channel opening.

In another example, with reference to FIGS. 14 a, 14 b, and 14 c , which illustrate sectional views and a perspective view of the irido-corneal angle 13, a surgical laser may scan ocular tissue in accordance with a second treatment pattern P2 designed to affect a surgical volume 901 (shown in two and three dimensions in FIG. 14 a ) to form a single, wide and shallow channel opening 921 (shown in two dimensions in FIG. 14 b and three dimensions in FIG. 14 c ). The shallow channel opening 921 extends from the Schlemm's canal 18, through the inner wall 18 a of the Schlemm's canal 18 and partially through the trabecular meshwork 12, so that only a portion of the tissue between the anterior chamber 7 and the Schlemm's canal is treated. In the example of FIGS. 14 a, 14 b, and 14 c , the shallow channel opening 921 extends through the juxtacanalicular tissue 17 and partially into the corneoscleral meshwork 16. In other treatment patterns, the shallow channel opening 921 may extend through the corneoscleral meshwork 16 and partially into the uveal 15.

In either case, the movement of the laser as it scans to affect the surgical volume 901 follows the second treatment pattern P2, which is defined by a set of surgical parameters that include a treatment area A and a thickness d. The treatment area A is defined by a width w and a height h. Again, the width may be defined in terms of a measure around the circumferential angle. For example, the width w may be defined in terms of an angle, e.g., 90 degrees around the circumferential angle.

An initial placement of the laser focus within the eye is defined by a set of placement parameters, including a depth d and a location l (not shown). The location l defines a point around the circumferential angle of the eye at which laser treatment will begin, while the depth d defines a point between the anterior chamber 7 and the Schlemm's canal 18 where the treatment begins or ends.

The channel opening 921 (FIGS. 14 b and 14 c ) resulting from laser application of the second treatment pattern P2 resembles the surgical volume 902 and is characterized by an area A and thickness t similar to those of the surgical volume and the treatment pattern. The depth d places an end of the surgical volume 902 in the corneoscleral meshwork 16. The thickness t of the resulting shallow channel opening 921 extends from the Schlemm's canal 18, through the inner wall 18 a of the Schlemm's canal and only partially into the trabecular meshwork 12, while the area A is such that the resulting shallow channel opening 921 (FIGS. 14 b and 14 c ) is characterized by a single opening.

In this example, the channel opening 921 has a first end in fluid communication with the Schlemm's canal 18 and a second end that terminates in a layer of ocular tissue between the anterior chamber 7 and the wall of the Schlemm's canal 18. The fluid communication may be enabled through a one or more lumens forming a pathway through the channel opening 921 and/or an arrangement of pores forming a porous pathway through the channel opening. In other configuration, the channel opening 921 may have a first end in fluid communication with the anterior chamber 7 and a second end that terminates in a layer of ocular tissue between the anterior chamber and the wall of the Schlemm's canal 18.

In yet another example, with reference to FIGS. 15 a, 15 b, and 15 c , which illustrate sectional views and a perspective view of the irido-corneal angle 13, a surgical laser may scan ocular tissue in accordance with a third treatment pattern P3 designed to affect an array of individual surgical volumes 903 (shown in two and three dimensions in FIG. 15 a ) to form a corresponding array of shallow sub-openings 923 (shown in two dimensions in FIG. 15 b and three dimensions in FIG. 15 c ). Each of the shallow sub-openings 923 extends from the Schlemm's canal 18, through the inner wall 18 a of the Schlemm's canal 18 and partially through the trabecular meshwork 12, so that only a portion of the tissue between the anterior chamber 7 and the Schlemm's canal is treated. The array of shallow sub-openings 923 collectively forming a sieve structure. In the example of FIGS. 15 a, 15 b, and 15 c , the sub-openings 923 extend through the juxtacanalicular tissue 17 and partially into the corneoscleral meshwork 16. In other treatment patterns, the sub-openings 923 may extend through the corneoscleral meshwork 16 and partially into the uveal 15.

In either case, the movement of the laser as it scans to affect the array of individual surgical volumes 903 follows the third treatment pattern P3, which is defined by a set of surgical parameters that include a treatment area A and a thickness d. The treatment area A is defined by a width w and a height h and establishes an overall boundary within which lies an array of individual sub-treatment areas. The width w may be defined in terms of a measure around the circumferential angle. For example, the width w may be defined in terms of an angle, e.g., 90 degrees around the circumferential angle.

An initial placement of the laser focus within the eye is defined by a set of placement parameters, including a depth d and a location l (not shown). The location l defines a point around the circumferential angle of the eye at which laser treatment will begin, while the depth d defines a point between the anterior chamber 7 and the Schlemm's canal 18 where the treatment begins or ends.

Each sub-treatment area within the treatment area A is characterized by a cross-section defined by a geometric shape, e.g., rectangular, square, round. The individual shallow sub-openings 923 (FIGS. 15 b and 15 c ) resulting from laser application of the third treatment pattern P3 resembles the individual surgical volumes 903 and is characterized by sub-area A_(S) and thickness t similar to those of the surgical volume and the treatment pattern. The depth d places an end of the individual surgical volumes 903 in the corneoscleral meshwork 16. The thickness t of the resulting individual shallow sub-openings 923 extends from the Schlemm's canal 18, through the inner wall 18 a of the Schlemm's canal and only partially into the trabecular meshwork 12.

Different levels of aqueous flow conductivity between the anterior chamber 7 and the Schlemm's canal 18 may be obtained using different laser treatment patterns having different surgical parameter sets. For example, flow conductivity typically increases monotonically together with increases in one or more of treatment area A and thickness d. The dependence between overall flow conductivity and treatment patterns and surgical parameter sets can be found by modeling, empirically through clinical studies, successive approximation, or by a combination of these techniques. An example of modeling of treatment patterns is described later below in the Aqueous Flow Model section.

Non-Invasive Laser Surgery—Photodisruptive Laser Pneumatic Canaloplasty

Applying the foregoing femtosecond laser capabilities, another embodiment of the integrated surgical system 1000 improves outflow pathway conductivity through pneumatic expansion of the Schlemm's canal 18. Laser interaction with ocular tissue results in the formation of microscopic gas bubbles. The combined effect from multiple microscopic gas bubbles is a creation of excess gas and associated pressure in a macroscopic volume. The excess gas and associated excess pressure can propagate to regions of tissue relatively far from the location of the laser interaction. For example, excess gas can travel through porous ocular tissue into and along the Schlemm's canal 18, and along the collector channels 19. The excess pressure associated with the gas results in a pneumatic expansion of the ocular tissues of the aqueous outflow pathways, the Schlemm's canal 18, and the collector channels 19.

This pneumatic expansion may be utilized to open collapsed regions of the Schlemm's canal 18 and collector channels 19 and in general increase outflow for an IOP reducing effect. In this embodiment, the integrated surgical system 1000 directs and focuses the laser at the fluid inside the Schlemm's canal 18 or the collector channels 19 or in the voids of porous tissue without direct laser effect to the ocular tissue. An increase in aqueous outflow conductivity is achieved only through pneumatic expansion of the Schlemm's canal 18 and/or the collector channels 19 and ocular tissue without laser modification of ocular tissue. Importantly, avoidance of direct tissue damage by the laser minimizes healing responses and scar formation that would otherwise be invoked by laser-damaged tissue. In the absence of such scarring, the possibility of re-closure of the outflow pathways through the pneumatic expanded structures and tissue is avoided.

FIGS. 16 a and 16 b illustrate before-and-after sectional views of the irido-corneal angle, where a surgical laser beam 701 is directed to the interior of a partially collapses Schlemm's canal 18 (shown in FIG. 16 a ) to affect pneumatic expansion of the Schlemm's canal 18 (shown in FIG. 16 b ). In this case, the treatment pattern P4 may be defined by a treatment area A generally corresponding to a cross-sectional area of the Schlemm's canal 18 and a width w defined in terms of a measure around the circumferential angle. For example, the width w may be defined in terms of an angle, e.g., 90 degrees around the circumferential angle. The area A and width w of the treatment pattern P4 define a volume generally corresponding to an interior of the Schlemm's canal 18.

An initial placement of the laser focus within the eye is defined by a set of placement parameters, including a depth d and a location l (not shown). The location l defines a point around the circumferential angle of the eye at which laser treatment will begin, while the depth d positions the point of the laser focus within the Schlemm's canal 18. In an embodiment, one or more locations of the Schlemm's canal spaced apart around the circumferential angle may be selected for laser application. The locations may be selected based on images of the Schlemm's canal 18.

In one configuration, images of the Schlemm's canal 18 at a plurality of locations around at least a portion of the circumferential angle are obtained using, for example, OCT. Each of the images is processed to determine a measure of an anatomical feature of the Schlemm's canal 18. Such anatomical feature may be a cross-section of the Schlemm's canal 18 and the measures may correspond to a radius, diameter, or circumference of the canal. The images are evaluated relative to a threshold measure to determine if the location associated with the image should be designated for laser delivery. In one embodiment, the threshold measure is the radius, diameter, or circumference of a Schlemm's canal 18 that is indicative of an at least partially collapsed canal. If the corresponding measure derived from the patient's image is less than the threshold measure, the location from which the image was obtained is designated a location for laser beam delivery. The threshold measure may be a predetermined value derived from a clinical database of measures from patients similar to the patient being treated. The threshold measure may also be derived through an analysis of all images collected for the patient. For example, the threshold measure may correspond to the largest measure determined from the images of the patient's Schlemm's canal, or the average of the measures determined from the images of the patient's Schlemm's canal.

During treatment, microscopic gas bubbles created by the laser beam 701 coalesce to form larger volumes gas bubbles 930. As this bubble expands, it expands the Schlemm's canal 18 and the surrounding tissue. The gas bubbles 930 will dissolve in a few minutes in the fluids of the tissue, leaving the expanded Schlemm's canal behind with no gas and tissue fragments in it. The treatment is non-invasive and it can be repeated to obtain incremental reductions in IOP until a desired overall IOP reduction is achieved, all without the longer term decrease of treatment efficacy that often results from treatments involving tissue modification.

Pneumatic expansion of the Schlemm's canal 18 and/or the collector channels 19 typically results in an IOP reduction. Accordingly, in an embodiment of the integrated surgical system 1000, expansion of the Schlemm's canal 18 and/or the collector channels 19 may be monitored and used to control laser treatment, e.g., stop treatment when an acceptable expansion has been achieved or when a maximum allowable pneumatic expansion is reached. The maximum allowable pneumatic expansion is a level of expansion at or above which ocular tissue and structures may be damaged.

For example, in one configuration, the integrated surgical system 1000 may provide images of the Schlemm's canal 18 from which changes in expansion may be observed. To this end, one or both of the OCT imaging apparatus 300 and visual observation device 400 may continually output current cross-sectional OCT images or visual images of the Schlemm's canal 18 for display on a screen during laser treatment. The operating surgeon may observe these images during the treatment, and determine to stop the laser treatment when the images indicate that a cross-section dimension, e.g., diameter, radius, circumference, of the Schlemm's canal 18 has either: 1) increased relative to its preoperative size by a desirable amount, or 2) is approaching a measure corresponding to a level of expansion at or above which ocular tissue and structures may be damaged.

In another configuration, control of laser treatment is implemented by the integrated surgical system 1000. To this end, a processor of the integrated surgical system 1000 executes an algorithm that continuously processes OCT cross-sectional images or visual images of the Schlemm's canal 18 during treatment to obtain measures indicative of pneumatic expansion of the canal. The measures may be a cross-section dimension, e.g., diameter, radius, circumference, of the Schlemm's canal 18. The processor then evaluates the measures to determine if a criterion is satisfied. For example, a criterion may be a target cross-section dimension value or may be a percentage increase from a baseline cross-section dimension value. The baseline value may correspond to, for example, a preoperative cross-section dimension value. If the criterion is satisfied, e.g., the target value or the percentage increase is met, the processor stops the laser treatment. If the criterion is not satisfied, e.g., the target value or the percentage increase is not met, the processor allows the laser treatment to continue.

Aqueous Flow Model

In accordance with embodiments disclosed herein, treatment patterns for laser tissue modification may be modeled using an aqueous flow model derived from Goldmann's model. Goldmann's model (R. F. Brubaker, Experimental Eye Research 78 (2004) 633-637) describes the relation between the IOP, the aqueous flow rate and the flow resistance. The model is described by the equation: F=(Pi−Pe)*C+U, where:

-   -   F is the rate of entry of the newly formed aqueous humor into         the anterior chamber 7,     -   U is the rate of outflow of aqueous humor via all channels that         are IOP independent, such as the uveoscleral outflow,     -   Pi is the IOP, defined as the pressure within the anterior         chamber 7 relative to atmospheric pressure,     -   C is the collective hydraulic conductivity of all pressure         dependent pathways out of the anterior chamber 7, and     -   Pe is the extraocular pressure, i.e., a summation over a number         of discrete microscopic pressure channels that drain aqueous         humor.

This equation is essentially the Ohm's law for stationary fluid flow. In an analogy with electronics, F and U are analogous to electric currents, hydraulic pressure differentials are analogous to voltages and hydraulic conductivity is analogous to electronic conductivity, which is the inverse of electronic resistance. Goldmann's equation under a condition (Pi−Pe)*C=F−U=constant, shows that, under stationary conditions when the aqueous inflow rate F is constant, the pressure differential between the anterior chamber 7 and the outflow drain pressure (Pi−Pe) is inversely proportional to the collective hydraulic conductivity C.

FIG. 17 displays this dependence as a set of hyperbolas, each line corresponding to a different constant parameter F−U. Three parameters of the Goldmann's model can be measured in human patients: 1) Pi, the IOP within the anterior chamber 7, 2) F, the rate of flow through the anterior chamber 7, and 3) C, the collective hydraulic conductivity of all pressure dependent pathways out of the anterior chamber 7. In addition, the main component of the extraocular pressure Pe, i.e., the episcleral venous pressure, can be estimated. This data allows a doctor to determine an aqueous flow diagnosis for a given patient, represented by a particular curve from the set of curves in FIG. 17 . This curve can be used as a baseline for treatment.

The intraocular pressure Pi can be measured with tonometry. The aqueous humor flow F can be measured by fluorophotometry (See, e.g., Jones, R. F., Maurice, D. M., 1966. New methods of measuring the rate of aqueous flow in man with fluorescein. Exp. Eye Res. 5, 208-220). The collective hydraulic conductivity C or outflow facility can be measured by tonography, e.g., by the weighted tonometer technique (See, e.g., Grant, W. M., 1950. Tonographic method for measuring the facility and rate of aqueous flow in human eyes. Arch. Ophthalmol. 44, 204-214). The tonographic measurement takes approximately 4 minutes to obtain, which generally corresponds to the time necessary for the eye to stabilize after being subjected to additional pressure from the weighted tonometer. For preoperative assessment, it is important to diagnose the patient under the right conditions. Drug treatment for glaucoma reduces the aqueous inflow rate F. Therefore the aqueous inflow rate F measurement should be taken with the patient temporarily taken off of drugs, or the flow measurement should be corrected for any effects from IOP reducing drugs.

Once the parameters of the Goldmann's model has been established by preoperative measurements, the (Pi−Pe) vs. C hyperbola curve can be constructed as shown on FIG. 17 . This curve forms the basis for selection of surgical treatment pattern parameters, such as the treatment area A and the thickness d, for a desired outflow modification and IOP reduction.

Other studies (M. A. Johnstone; The Aqueous Outflow System as a Mechanical Pump; J Glaucoma 2004; 13:421-438) indicate evidence of tissue structures and mechanotransduction mechanisms within the trabecular meshwork 12 and the Schlemm's canal 18, which, through tissue deformation coupled to aqueous flow, are capable of providing feedback mechanisms to regulate IOP. These control mechanisms are not fully understood yet and cannot be described with the simple Goldmann's model. A combined model can include a controlled portion of the aqueous flow added to the Goldmann's model.

With reference to FIG. 18 , developing the electronics analogy further, a circuit diagram can be constructed for the aqueous flow. The circuit diagram may be described in terms of rows and columns, where each row is presented by like types of circuit components, e.g., Ru1+Ru2 . . . +Run, Rsc1+Rsc2 . . . +Rscn, etc., and each columns by one of every type of circuit component, e.g., Ru1+Rsc1+Rj1+Rs1+Rc1. In this diagram, constant current sources with currents F and U, respectively represent the aqueous inflow rate F and the pressure independent part of the aqueous outflow U. The inflow current F is split to three paths, Uc, U and T. These four components are defined by the following equation: T=F−U−Uc, where

-   -   F is the rate of entry of the newly formed aqueous humor into         the anterior chamber 7 (F from Goldmann's equation)     -   U is the rate of outflow of aqueous humor via all channels that         are IOP independent, such as the uveoscleral outflow (U from         Goldmann's equation)     -   Uc is the portion 1400 of the trabecular outflow, which is         controlled by feedback mechanisms of the eye, and     -   T is the trabecular flow current, represented in FIG. 18 by a         current meter test point 1401.

With reference to FIG. 4 , T is represented by graphical arrow 40 and U is represented by arrow 42. This representation on FIG. 4 is schematic, since in the Goldmann's model U represents all pressure independent outflow channels, not just the uveoscleral outflow 42. Several clinical studies indicate that the amount of the pressure independent flow U is approximately 10 percent of the aqueous inflow rate F. Nevertheless, U and T are also labeled in FIG. 18 with callouts 42 and 40. On the circuit diagram the lower equipotential line 7 represents the IOP Pi, while the higher equipotential line 31 represents the extraocular pressure Pe. A voltage source 1402, represents a constant voltage source maintaining the potential difference Pi−Pe. Resistors represent the inverse of hydraulic conductivities of tissue.

With regards to the biomechanical properties, the ocular tissue is continuous. FIG. 18 is a discretized model of the continuous tissue media. The volume of tissue is divided into small segments, labeled with an index i, i=1 . . . n. If the segments are sufficiently small, the discrete representations accurately describe the continuous properties of the media. For example, in the case where n=360, the circuit diagram may represent the entirety of the circumferential angle, where each segment indexed from i=1 to 360 corresponds to a one-degree segment of the 360 degree circumferential angle. Tissue division and indexing can further include division along other geometrical dimensions. Finite element modeling software such as ANSYS from Ansys Inc., Canonsburg, Pa. or COMSOL from COMSOL Inc., Burlington, Mass. can routinely handle this type of modeling and the solution of the corresponding equations. The resistors Ru, Rcs and Rj respectively represent the three sub-layers of the trabecular meshwork 12: the uveal 15, the corneoscleral meshwork 16 and the juxtacanalicular tissue 17. Resistors Rsi represent the Schlemm's canal 18. Note that Rs1 and Rsn are connected by a line, indicating that the Rsi resistors form a circle, thus modeling the circular shape of the Schlemm's canal 18. Resistors Rc represent the collector channels 19.

Precise Control of IOP with Surgery

With reference to FIGS. 19 a, 19 b, and 19 c , different treatment patterns may be modeled using the circuit diagram of FIG. 18 . For example, the treatment pattern P1 resulting in the deep channel opening 920 shown in FIG. 11 b may be modeled by changing the values of the resistors Ru, Rcs and Rj (corresponding respectively to the uveal 15, the corneoscleral meshwork 16 and the juxtacanalicular tissue 17) to zero in the area 920 shown in FIG. 19 a . In the circuit model, the area 920 may be described as being two columns wide and three rows deep, where the number of columns defines the width w of the treatment pattern, and the number of rows defines the thickness t of the treatment pattern.

The treatment pattern P2 resulting in the shallow channel opening 921 shown in FIG. 14 b may be modeled by changing the values of the resistors Rj (corresponding to the juxtacanalicular tissue 17) to zero in the area 921 shown in FIG. 19 b . In the circuit model, the area 921 may be described as being two columns wide and one row deep, where the number of columns defines the width w of the treatment pattern, and the number of rows defines the thickness t of the treatment pattern.

The treatment pattern P4 resulting in the pneumatic expansion 930 of the Schlemm's canal 18 shown in FIG. 16 b may be modeled by reducing the value of the resistors Rs (corresponding to the Schlemm's canal 18) to zero in the area 931 shown in FIG. 19 c . In the circuit model, the area 931 may be described as being two columns wide and one row deep, where the number of columns defines the width w of the treatment pattern, and the number of rows defines the thickness t of the treatment pattern.

Patterns with other geometric shapes can be modeled in the circuit diagram and through finite element analysis in a similar manner.

In embodiments disclosed herein, an initial treatment pattern characterized by a set of surgical parameters that define the size and shape of tissue modifications (or surgical cuts) for a desired change in aqueous outflow is determined. Laser treatment in accordance with the initial treatment pattern is delivered and the clinical outcome is determined. If the clinical outcome is acceptable, the treatment is ended; otherwise a subsequent treatment pattern is determined and laser treatment is repeated.

FIG. 21 is a flowchart of a method of designing a treatment pattern using the aqueous flow model of FIG. 18 . The method may be performed by one or more components of the integrated surgical system 1000 of FIGS. 7-10 b. For example, the control system 100 may include a processor and a memory coupled to the processor that stores instructions that enable the processor to execute or implement the method of FIG. 21 . The method of FIG. 21 may also be performed by a processor and memory that are separate from the integrated surgical system 1000.

At step 1500, preoperative outflow parameters of the eye to be treated are obtained or derived. These measures include preoperative measures of: 1) the IOP within the anterior chamber, 2) the collective hydraulic conductivity C, and 3) the flow resistance of the Schlemm's canal Rs. The IOP can be obtained using known techniques. The collective hydraulic conductivity C may be determined from preoperative IOP measurements and weighted tonometry. The flow resistance of the Schlemm's canal Rs may be determined by measuring the canal's cross-section with the OCT imaging apparatus 300 and applying the hydrodynamic flow equation for laminar flow of the aqueous within the canal. For a Schlemm's canal 18 assumed to have a circular cross section, analytical formula can be applied. For arbitrary cross sections, flow resistance can be calculated by finite element analysis, for example by ANSYS or COMSOL.

At step 1502, the outflow parameters are applied to an electrical circuit model of aqueous flow. To this end, the flow model of FIG. 18 may be simplified, based on the preoperative measurements and data from studies on relative contribution of flow resistance from different tissues in the eye. For example, studies indicate that the resistance through the trabecular meshwork 12 is concentrated at the inner wall 18 a of the Schlemm's canal 18 and the juxtacanalicular tissue 17. See, for example, Hann C R, Vercnocke A J, Bentley M D, Jorgensen S M, Fautsch M P. Anatomic changes in Schlemm's canal and collector channels in normal and primary open-angle glaucoma eyes using low and high perfusion pressures. Invest Ophthalmol Vis Sci. 2014; 55:5834 5841. DOI:10.1167/iovs.14-14128; Rosenquist R, Epstein D, Melamed S, Johnson M, Grant W M. Outflow resistance of enucleated human eyes at two different perfusion pressures and different extents of trabeculotomy. Curr Eye Res. 1989; 8:1233-1240. Further, these studies attribute up to 50% of outflow resistance to the Schlemm's canal 18, collector channels 19, and the episcleral venous system at low perfusion pressures, and lesser but significant outflow resistance effects due to these components at higher perfusion pressures. Based on these studies, the flow model of FIG. 18 may be simplified by assuming the uveal 15 and the corneoscleral meshwork 16 do not contribute to the outflow resistance and thus, eliminating the Ru resistors and the Rcs resistors from the diagram. This simplified model is shown in FIG. 20 a.

Continuing with step 1502 and the simplified model of FIG. 20 a , the modeling process continues by solving for components of the circuit diagram. Rci and Rji are determined from the relationship C=1/R, where R is the combined resistance of all indexed resistors Rc, Rs, Rj, and C corresponds to the collective hydraulic conductivity obtained in step 1500. Further, assuming circular symmetry, then the indexed resistances of the particular tissue are all the same, where circular symmetry corresponds to a condition where the Schlemm's canal 18 has the same cross section along the circumferential angle, the trabecular meshwork 12 has the same thickness and porosity along the circumferential angle and the collector channels 19 are distributed evenly along the circumferential angle. In this case, the resistors Rsi of the Schlemm's canal are on an equipotential surface. And on an equipotential surface there is no current flowing parallel to the surface. It is further assumed that in case of a disease affecting the flow resistance, say clogging the pores of the trabecular meshwork, the disease affects the tissue the same way along the circumferential angle. Based on the foregoing, in the diagram of FIG. 20 a , Rj1=Rj2= . . . =Rjn, Rc1=Rc2= . . . =Rcn and Rs1=Rs2= . . . Rsn.

A further simplified model is illustrated in FIG. 20 b , wherein all Rs values can be eliminated, since there is no flow in the Schlemm's canal 18 in the symmetrical case. In this context, “no flow” refers to the condition where there is no circumferential flow of aqueous within the Schlemm's canal 18. No flow does not preclude the natural flow of aqueous from the trabecular meshwork 12 through the canal 18 and directly into the collector channels 19. Continuing with FIG. 20 b , this simplified model can now be solved to determine values of Rc and Rj. With equal weighting of the trabecular and collector channel resistance, Rci=Rji=n/2C, where n is an arbitrary number, for example 360 for 1 degree resolution along the circumferential angle, and C is the collective hydraulic conductivity obtained in step 1500. This solution of the equation can only be obtained with the assumption of the circular symmetry and elimination of Rs.

At step 1504, the simplified model of FIG. 20 a is modified based on a test treatment pattern and known circuit component values. For example, with reference to FIG. 20 c , a test treatment pattern similar to the treatment pattern P2 shown in FIGS. 14 b and 14 c may be modeled by setting the values of the Rj resistors to zero in the area 921 and the remainder of the Rj resistors to the value obtained in step 1502. The Rc resistors are also set to the value obtained in step 1502, while the Rs resistors are set to the value obtained in step 1500. After setting the values of the Rj resistors to zero in the area 921, the assumption of circular symmetry no longer holds true, due to the zero values of the Rj resistors in the area 921.

At step 1506, a measure of IOP is obtained based on the model. This measure is referred to herein as a model IOP. Having thus modeled a test treatment pattern as shown in the circuit diagram model of FIG. 20 c , the process returns to the circuit diagram model of FIG. 20 a where the outflow drain pressure (Pi−Pe) from Goldmann's equation that would result from the test treatment pattern of FIG. 20 c is calculated. This outflow drain pressure is referred to herein as surgically modified pressure or postoperative pressure and is noted as (Pi−Pe)postop. The process returns to the model of FIG. 20 a because with a surgical opening at a particular location, such as shown in the model of FIG. 20 c , circular symmetry may no longer be assumed. Thus the simplification Rj1=Rj2= . . . =Rjn, Rc1=Rc2= . . . =Rcn and Rs1=Rs2= . . . Rsn no longer applies and it is thus necessary to solve the model for an asymmetrical case.

To this end, the respective values for Rji, Rsi and Rci resistors obtained in steps 1500 and 1502 are used at the respective resistors locations where the tissue is left intact, and the value Rji=0 is used in the area 921 where tissue would be modified to create a channel opening. The postoperative pressure (Pi−Pe)postop may be determined by inserting the new combined resistance Rpostop=1/Cpostop and the preoperative flow F−U back into the Goldmann's equation and solving the equation (Pi−Pe)postop=(F−U)*Rpostop. In this process it is assumed that the flow rate F−U is not modified by the surgery. Similarly, the extraocular pressure Pe, does not depend on the surgical effects made on the trabecular meshwork 12 and the Schlemm's canal 18 because the preoperative extraocular pressure (Pe)preop is equal to the postoperative extraocular pressure (Pe)postop. Therefore, the change of the intraocular pressure ΔPi=(Pi−Pe)postop−(Pi−Pe)preop. The actual value of the extraocular pressure Pe is not needed for the determination of the change of the intraocular pressure ΔPi. The change of the intraocular pressure ΔPi may be used as the modeled IOP. Alternatively, based on the relationship ΔPi=(Pi)preop−(Pi)postop, and having known values for ΔPi and (Pi)preop, a value for (Pi)postop may be obtained.

At step 1508, the model IOP is evaluated relative to the target IOP. For example, the value of ΔPi may be compared to a target IOP corresponding to an desired reduction in IOP, such as a 5 mm Hg reduction. Or a value for (Pi)postop may be compared to a target IOP corresponding to a desired value of IOP, such as a 15 mm Hg. At step 1510, if the evaluation outcome is positive, meaning the model IOP satisfied the target IOP, the modeling process ends at step 1512. If, however, the evaluation outcome is negative at step 1510, meaning model IOP did not satisfy the target IOP, the modeling process returns to step 1504, where the test treatment pattern is modified and the remainder of the process is repeated. The test treatment pattern may be modified iteratively until the target IOP is achieved.

The method described to determine an initial treatment pattern is specific to individual patients, based on their preoperative diagnosis. To perform the surgical treatment, the initial treatment pattern is programmed into the control system 100 of the surgical system 1000 and laser treatment is delivered in accordance with the treatment pattern to excise or affect a surgical volume, as described in previous paragraphs and according to the flowchart of FIG. 12 .

Alternatively, the initial treatment pattern can be determined by considering empirical results from previous surgeries with femtosecond laser or ELT surgery. Collection of sufficient amounts of data allows the construction of a nomogram, where treatment patterns and associated sets of surgical parameters can be quickly determined or looked up by graphical association to charted or tabulated data. Computer algorithms can also utilize data from previous surgeries to construct a surgical plan.

FIG. 22 is a flow chart of a method of achieving precise IOP reduction in successive multiple steps of IOP measurements and surgery. The method may be performed by one or more components of the integrated surgical system 1000 of FIGS. 7-10 b. For example, the control system 100 may include a processor and a memory coupled to the processor that stores instructions that enable the processor to execute or implement the method of FIG. 22 .

At step 1600, an IOP criterion is determined for the patient. An IOP criterion may be a target IOP that is considered an acceptable outcome for the patient. Another IOP criterion may be a threshold reduction in a current IOP relative to an elevated, preoperative IOP of the patient, that considered an acceptable outcome for the patient. The IOP criterion may be based on actual measures of IOP obtained from the patient. For example, an IOP in the range of 12 to 22 mm Hg is considered normal. Accordingly, a target IOP may correspond to 12 to 22 mm Hg. A threshold reduction in IOP may correspond to, for example, at least a 20% reduction from an elevated, preoperative IOP of the patient. Yet another IOP criterion may be a minimum IOP needed to avoid harming the eye. For example, the IOP should not drop below 10 mm Hg, where the eye is considered hypotonous. Postoperative hypotony can lead to engorged retinal vessels, swollen optic discs, and folds in the choroid and retina.

In another configuration, the IOP criterion may be based on anatomical dimensional measures that function as surrogates for actual IOP measures. As described above with reference to FIGS. 16 a and 16 b , a cross-section dimension, e.g., diameter, radius, circumference, or cross sectional area of the Schlemm's canal 18 may serve as a measure of IOP. For example, the Schlemm's canal 18 having a cross sectional area 4064+/−1308 μm², as measured by comprehensive spectral domain OCT is considered normal. (Kagemann L, et al. Br J Ophthalmol 2014, 98(Suppl II):ii10-ii14) Accordingly, a target IOP may correspond to a cross sectional area in the range of 2756 to 5372 μm². A threshold reduction in IOP may correspond to, for example, at least a 30% increase in the cross sectional area of the Schlemm's canal 18 from a preoperative cross sectional area of the patient. Yet another IOP criterion may be a maximum diameter that must not be exceeded in order to avoid harming the eye.

At step 1602, an OCT beam 301 is delivered through the cornea 3 and the anterior chamber 7 into the irido-corneal angle 13. In one embodiment, the OCT beam 301 has a resolution less than or equal to approximately 5 micrometers and is delivered to the irido-corneal angle 13 by directing the OCT beam to a first optical subsystem 1001 that includes a window 801 coupled to the cornea 3 and an exit lens 710 coupled to the window.

At step 1604, an OCT image of a portion of the irido-corneal angle 13 is acquired based on the OCT beam 301 delivered to the irido-corneal angle through the first optical subsystem 1001. To this end, an OCT return beam 301 is received through the first optical subsystem 1001 and processed at an OCT imaging apparatus 300 using known OCT imaging techniques.

At step 1606, an initial treatment pattern P1, P2, P3 is determined or designed together with a corresponding location within the eye for laser application of the initial treatment pattern. The initial treatment pattern may be designed in accordance with the method of FIG. 21 . The treatment pattern may be defined by a set of parameters including a treatment area A and a treatment thickness t. The treatment area A may be defined by a height h and a width w, where the width may be defined in terms of a measure around the circumferential angle. The location l indicates that location around the circumferential angle where laser application of the treatment patter is to occur. The pattern may be designed, for example using the aqeuous flow model described above, to satisfy an IOP criterion. For example, an IOP criterion may represent a goal of reducing the patient's preoperative IOP by a certain percentage. As previously described, the treatment pattern P1, P2, P3 defines a three-dimensional model of ocular tissue to be modified by a laser. Thus, a laser that modifies tissue in accordance with a treatment pattern P1, P2, P3 affects or produces a surgical volume 900, 901, 903 that resembles the three-dimensional model of the treatment pattern.

At step 1608, each of an OCT beam 301 and a laser beam 201 is delivered through the cornea 3, and the anterior chamber 7 into the irido-corneal angle 13. In one embodiment, the OCT beam 301 and laser beam 201 have substantially equal resolutions, e.g., less than or equal to approximately 5 micrometers, and each beam is delivered to the irido-corneal angle by directing each beam to a first optical subsystem 1001 that includes a window 801 coupled to the cornea 3 and an exit lens 710 coupled to the window. The OCT beam 301 and the laser beam 201 may be collinearly directed to the first optical subsystem 1001 along a same optical path, for example by multiplexing the beams. Alternatively, the OCT beam 301 and the laser beam 201 may be non-collinearly directed to the first optical subsystem at the same time along spatially separated or angled optical paths.

At step 1610, in one embodiment, a laser beam 201 is applied in accordance with the initial treatment pattern P1, P2, P3 to modify a volume 900, 901, 903 of ocular tissue within the trabecular outflow pathway 40 to create a channel opening that reduces a pathway resistance present in one or more of the trabecular meshwork 12, the Schlemm's canal 18, and the one or more collector channels 19. To this end, a laser beam 201 having a wavelength between 330 nanometers and 2000 nanometers may be scanned in multiple directions in accordance with the initial treatment pattern to thereby affect or produce a surgical volume 900, 901, 903 that resembles three-dimensional model of the initial treatment pattern P1, P2, P3.

The laser beam 201 may be applied in a continuous manner or as a multitude of laser pulses with a pulse duration between 10 femtoseconds and 1 nanosecond. The laser beam 201 causes photo-disruptive interaction with the ocular tissue to reduce the pathway resistance or create a new outflow pathway 40. Depending on the initial treatment pattern, photo-disruptive interaction with the ocular tissue may create, for example: 1) a deep channel opening 920 opened through the trabecular meshwork connecting the anterior chamber and the Schlemm's canal, such as shown FIG. 11 b, 2) a shallow channel opening 921 that extends through the juxtacanalicular tissue 17 and partial into the corneoscleral meshwork 16, such as shown in FIG. 14 b , or 3) an array of shallow sub-openings 923 that extend through the juxtacanalicular tissue 17 and partial into the corneoscleral meshwork 16 such as shown in FIG. 15 b . Numerous types of channel openings may be created based on different designs of treatment patterns.

In another embodiment, at step 1610 a laser beam 201 is applied in accordance with the initial treatment pattern to produce a pneumatic expansion of the Schlemm's canal 18, and the one or more collector channels 19 by applying the laser beam 201 to the interior of the canal. The initial treatment pattern places the focus of the laser beam 201 inside of the Schlemm's canal 18 to avoid modification of ocular tissue. The laser beam 201 has a wavelength between 330 nanometers and 2000 nanometers and is scanned in accordance with the surgical parameters of the initial treatment pattern to thereby form microscopic gas bubbles that affect a pneumatic expansion of the Schlemm's canal 18 as described above with reference to FIG. 16B.

At step 1612, after a short period of time to allow the aqueous flow to stabilize in the eye, a current, postoperative IOP measure, e.g., an actual IOP measure or an anatomical measure, is obtained and evaluated against the IOP criterion determined at step 1600. At step 1614, if the evaluation outcome at step 1612 is acceptable, the process proceeds to step 1616, where the surgical procedure is ended. An evaluation outcome may be acceptable, for example, when the postoperative IOP is at or below a target IOP, or when the postoperative IOP represents an acceptable reduction relative to the patient's preoperative IOP.

Returning to step 1614, if the evaluation outcome is not acceptable, the process proceeds to step 1618 to determine a subsequent treatment pattern and corresponding location in the eye for laser application of the treatment pattern. Steps 1608 and 1610 are then repeated using the subsequent treatment pattern, followed by evaluation steps 1612 and 1614. These successive steps of treatment pattern modification, laser treatment and evaluation can be repeated again until the evaluation outcome of steps 1612 and 1614 is acceptable.

Regarding step 1618, the subsequent treatment pattern may be determined using the aqueous flow model method of FIG. 21 used to determine the initial treatment pattern. Alternatively, the subsequent treatment pattern may be based on the initial treatment pattern with changes in one or more of the surgical parameters of the initial treatment pattern. For example, the subsequent treatment pattern may have the same treatment area A as the initial treatment pattern, but an increased thickness d. Or the thickness t of the new treatment pattern may be the same as the initial treatment pattern with an increase in treatment area A. The subsequent location l for the subsequent treatment pattern may locate the pattern anywhere around the circumferential angle of the eye. For example, the location l may place the subsequent treatment pattern 180 degrees around the circumferential angle from the initial treatment pattern, or a number of degrees that locates the pattern closer to the initial treatment pattern. In some cases the subsequent treatment pattern may be located immediately adjacent to the initial treatment pattern or located so that it partially overlaps with the initial treatment pattern. In some instances, the subsequent treatment pattern may be the same as the initial treatment pattern, with the only change being a change in location l around the circumferential angle.

A change in the IOP can be observed within several minutes after surgery and it may take several days for the IOP to stabilize. Therefore, it is advantageous to wait between successive steps of surgery. Stabilization of the IOP involves several processes and there are several timescales involved. Mechanical disturbance to the eye occurs when attaching the surgical system 1000 to the eye, or by weighted tonometry. It takes several minutes, up to ten minutes, for the eye to stabilize after these mechanical disturbances. Gas bubbles created by the laser may prevent postoperative assessment until the gas is dispersed and dissolved within the ocular tissue. Gas dissolves in the tissue in less than approximately 30 minutes. Stabilization of the eye after the short term disturbances allow retreatment during the same day, not requiring re-scheduling the patient for a second visit to the treatment facility. Cellular responses to trauma, immune response and inflammation may take a day to start and several days to clear. Therefore, it does not significantly affect IOP measurement taken the same day after the surgery. Long term healing effects can last for several months after surgery. These time scales are considered for the weighting period between successive surgeries, re-evaluations and re-treatments. Multiple measurements at different times facilitate achieving higher accuracy and prediction of anticipated IOP values at future times.

The various aspects of this disclosure are provided to enable one of ordinary skill in the art to practice the present invention. Various modifications to exemplary embodiments presented throughout this disclosure will be readily apparent to those skilled in the art. Thus, the claims are not intended to be limited to the various aspects of this disclosure, but are to be accorded the full scope consistent with the language of the claims. All structural and functional equivalents to the various components of the exemplary embodiments described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 U.S.C. § 112, sixth paragraph, unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited using the phrase “step for.”

It is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention. 

What is claimed is:
 1. A method of designing an initial treatment pattern that defines an initial volume of ocular tissue of an eye to be modified by scanning a laser through the initial treatment pattern to thereby photo disrupt the initial volume of ocular tissue, wherein the initial volume of ocular tissue comprises a trabecular meshwork comprising a uveal layer, a corneoscleral meshwork, and a juxtacanalicular tissue, and the initial treatment pattern is defined by a set of surgical parameters, the method comprising: obtaining a plurality of preoperative outflow parameters of the eye; modeling aqueous flow through the trabecular meshwork with an electrical circuit having discrete sets of electrical circuit components, wherein each discrete set of electrical circuit components models one of the uveal layer, the corneoscleral meshwork, and the juxtacanalicular tissue; applying one or more of the plurality of preoperative outflow parameters to the electrical circuit model of aqueous flow; solving for values of one or more of the electrical circuit components based on at least one of the plurality of preoperative outflow parameters; modifying the electrical circuit model of aqueous flow based on a test treatment pattern and the values of the one or more of the electrical circuit components; obtaining a model intraocular pressure (IOP) based on the modified electrical circuit model of aqueous flow; evaluating the model IOP relative to an IOP criterion to obtain an evaluation outcome; when the evaluation outcome is positive, designating the test treatment pattern as an initial treatment pattern, and providing the set of surgical parameters that define the initial treatment pattern to a control system configured to control the scanning of the laser based on the initial treatment pattern; and when the evaluation outcome is negative, modifying the electrical circuit model of aqueous flow based on a modified test treatment pattern, and repeating the obtaining and the evaluating.
 2. The method of claim 1, wherein the plurality of preoperative output flow parameters of the eye comprises a measure of hydraulic flow resistance of a Schlemm's canal and obtaining the measure comprises: measuring a cross sectional dimension of the Schlemm's canal; and applying a hydrodynamic flow equation for laminar flow of the aqueous within the Schlemm's canal.
 3. The method of claim 2, wherein the cross sectional dimension of the Schlemm's canal is obtained from at least one of a light microscopy image and an optical coherence tomography (OCT) image of the eye.
 4. The method of claim 1, wherein the plurality of preoperative output flow parameters of the eye comprises one or more of a measure of IOP, and a measure of collective hydraulic conductivity.
 5. The method of claim 1, wherein obtaining a model IOP based on the modified electrical circuit model of aqueous flow comprises determining a hydraulic flow resistance through a trabecular meshwork of the eye.
 6. The method of claim 1, wherein the IOP criterion corresponds to either of a target measure of IOP or a target reduction in IOP, and evaluating the model IOP relative to an IOP criterion comprises: determining the evaluation outcome is positive when the model IOP is less than or equal to the target measure of IOP; and determining the evaluation outcome is positive when a difference between the model IOP and a preoperative measure of IOP is greater than or equal to the target reduction in IOP.
 7. A control system for designing an initial treatment pattern that defines an initial volume of ocular tissue of an eye to be modified by a surgical system having a control system configured to scan a laser through the initial treatment pattern to thereby photo disrupt the initial volume of ocular tissue, wherein the initial volume of ocular tissue comprises a trabecular meshwork comprising a uveal layer, a corneoscleral meshwork, and a juxtacanalicular tissue, and the initial treatment pattern is defined by a set of surgical parameters, the control system comprising: a memory; and at least one processor coupled to the memory and configured to: model aqueous flow through the trabecular meshwork with an electrical circuit having discrete sets of electrical circuit components, wherein each discrete set of electrical circuit components models one of the uveal layer, the corneoscleral meshwork, and the juxtacanalicular tissue; apply one or more of a plurality of preoperative outflow parameters of the eye to the electrical circuit model of aqueous flow; solve for values of one or more of the electrical circuit components based on at least one of the plurality of preoperative outflow parameters; modify the electrical circuit model of aqueous flow based on a test treatment pattern and the values of the one or more of the electrical circuit components; obtain a model intraocular pressure (IOP) based on the modified electrical circuit model of aqueous flow; evaluate the model IOP relative to an IOP criterion to obtain an evaluation outcome; when the evaluation outcome is positive, designate the test treatment pattern as the initial treatment pattern and provide the set of surgical parameters that define the initial treatment pattern to the control system; and when the evaluation outcome is negative, modify the electrical circuit model of aqueous flow based on a modified test treatment pattern, and repeat the obtaining and the evaluating.
 8. The control system of claim 7, wherein the plurality of preoperative output flow parameters of the eye comprises a measure of hydraulic flow resistance of a Schlemm's canal, and the at least one processor is configured to obtain the measure by being configured to: measure a cross sectional dimension of the Schlemm's canal; and apply a hydrodynamic flow equation for laminar flow of the aqueous within the Schlemm's canal based on the measured cross sectional dimension.
 9. The control system of claim 8, wherein the cross sectional dimension of the Schlemm's canal is measured by the at least one processor from at least one of a light microscopy image received from a visual observation apparatus and an OCT image received from an optical coherence tomography (OCT) imaging apparatus.
 10. The control system of claim 7, wherein the plurality of preoperative output flow parameters of the eye comprises one or more of a measure of IOP, and a measure of collective hydraulic conductivity.
 11. The control system of claim 7, wherein the at least one processor obtains a model IOP based on the modified electrical circuit model of aqueous flow by being further configured to determine a hydraulic flow resistance through a trabecular meshwork of the eye.
 12. The control system of claim 7, wherein the IOP criterion corresponds to either a target measure of IOP or a target reduction in IOP, and the at least one processor evaluates the model IOP relative to an IOP criterion by being further configured to: determine the evaluation outcome is positive when the model IOP is less than or equal to the target measure of IOP; and determine the evaluation outcome is positive when a difference between the model IOP and a preoperative measure of IOP is greater than or equal to the target reduction in IOP.
 13. The control system of claim 7, wherein the at least one processor is configured to: obtain a plurality of IOP measures at different times within a period after an initial laser treatment; and derive a postoperative measure of IOP based on the plurality of IOP measures.
 14. The control system of claim 7, wherein the IOP criterion corresponds to either a target measure of IOP or a target reduction in IOP, and the processor evaluates a postoperative measure of IOP relative to an IOP criterion by being further configured to: determine the IOP criterion is satisfied when the postoperative measure of IOP is less than or equal to the target measure of IOP; and determine the IOP criterion is satisfied when a difference between the postoperative measure of IOP and a preoperative measure of IOP is greater than or equal to the target reduction in IOP.
 15. The control system of claim 7, wherein the initial treatment pattern is defined by a set of surgical parameters comprising an area and a thickness, and determining a subsequent treatment pattern comprises modifying one or more of the area or the thickness.
 16. A method of designing a treatment pattern through which a laser beam is scanned to photo disrupt a volume of ocular tissue of an eye, wherein the volume of ocular tissue comprises a trabecular meshwork comprising a uveal layer, a corneoscleral meshwork, and a juxtacanalicular tissue, and the treatment pattern is defined by a set of surgical parameters, the method comprising: modeling aqueous flow through the trabecular meshwork with an electrical circuit having discrete sets of electrical circuit components, wherein each discrete set of electrical circuit components models one of the uveal layer, the corneoscleral meshwork, and the juxtacanalicular tissue; applying one or more of a plurality of preoperative outflow parameters to the electrical circuit model of aqueous flow; solving for values of one or more of the electrical circuit components based on at least one of the plurality of preoperative outflow parameters; modifying the electrical circuit model of aqueous flow based on a test treatment pattern and the values of the one or more of the electrical circuit components; obtaining a model intraocular pressure (IOP) based on the modified electrical circuit model of aqueous flow; evaluating the model IOP relative to an IOP criterion to obtain an evaluation outcome; when the evaluation outcome is positive, designating the test treatment pattern as the treatment pattern and providing the set of surgical parameters that define the treatment pattern to a control system configured to control the scanning of the laser based on the treatment pattern; and when the evaluation outcome is negative, modifying the electrical circuit model of aqueous flow based on a modified test treatment pattern, and repeating the obtaining and the evaluating.
 17. An apparatus for designing a treatment pattern through which a laser beam is scanned to photo disrupt a volume of ocular tissue of an eye, wherein the volume of ocular tissue comprises a trabecular meshwork comprising a uveal layer, a corneoscleral meshwork, and a juxtacanalicular tissue, and the treatment pattern is defined by a set of surgical parameters, the apparatus comprising: a memory; and at least one processor coupled to the memory and configured to: model aqueous flow through the trabecular meshwork with an electrical circuit having discrete sets of electrical circuit components, wherein each discrete set of electrical circuit components models one of the uveal layer, the corneoscleral meshwork, and the juxtacanalicular tissue; apply one or more of a plurality of preoperative outflow parameters to the electrical circuit model of aqueous flow; solve for values of one or more of the electrical circuit components based on at least one of the plurality of preoperative outflow parameters; modify the electrical circuit model of aqueous flow based on a test treatment pattern and the values of the one or more of the electrical circuit components; obtain a model intraocular pressure (IOP) based on the modified electrical circuit model of aqueous flow; evaluate the model IOP relative to an IOP criterion to obtain an evaluation outcome; when the evaluation outcome is positive, designate the test treatment pattern as the treatment pattern and provide the set of surgical parameters that define the treatment pattern to a control system configured to control the scanning of the laser based on the treatment pattern; and when the evaluation outcome is negative, modify the electrical circuit model of aqueous flow based on a modified test treatment pattern, and repeat the obtaining and the evaluating. 